With the appeal coming up at the end of this month, there has been a lot of news about the apparent weaknesses of the DNA evidence used to convict Amanda Knox and her boyfriend Raffaele Sollecito in the murder of Meredith Kercher. After a Twitter discussion with Doug Bremner (dougbremner.com) I was inspired to learn more about the case and offer some insight on some of the DNA issues.  I quickly learned that there is a veritable ton of information online about the case, and I have included some helpful links at the end of this post.

This case is a defense DNA expert’s dream! I would love to have access to the testing results, notes, data, procedures, etc. and compose a cross-examination for the Italian forensic scientist who performed the work. There are several influential DNA experts from the U.S. that have weighed in on this case already. Having said that, let me offer the standard disclaimer that I am not an official expert on the case and have not seen actual data, protocols, reports, etc.  I have therefore decided to touch just generally on the apparent evidence and facts of the case, and focus more on overall themes and concepts that are common to many DNA cases.  I hope that this will provide valuable insight to the public.

First, let me lay the groundwork by noting some of the basic apparent facts of the case.  Meredith Kercher was found murdered with slash wounds to the throat at her residence.  Her body was found partially disrobed and there was evidence of sexual assault.  Amanda Knox was Meredith Kercher’s roommate.  Ms. Knox’s boyfriend, Raffaele Sollecito was also convicted of the crime.  The first individual to be convicted was Rudy Guede.  DNA tests from the body and from a bloody fingerprint in the room came back to Guede, and there was apparently no question as to his involvement.  However, the Italian authorities surmised that this criminal act also included involvement from Knox and Sollecito. The key pieces of physical evidence proffered as showing their involvement were a knife found at Sollecito’s residence and Kercher’s bra clasp found at the crime scene. Knox and Sollecito were convicted and sentenced to approximately 25 years each.



A knife collected from Sollecito’s residence was tested for blood and DNA.  No blood was detected on the knife.  DNA testing of a swab from the handle apparently was consistent with Amanda Knox. Without having reports, data, etc. it is not clear to me how strong of an association was found to Knox, but let’s assume that they obtained unequivocal results demonstrating the presence of her DNA on the handle.  Considering the fact that she was known to spend time at the apartment and cook, the finding of her DNA on the handle is of no particular probative value. Consider also, that there is no way to date when the DNA consistent with Knox was deposited on the knife handle.  With the increased sensitivity of modern DNA testing, items that have simply been touched, or handled (like the keyboard you are using now) will contain detectable amounts of DNA.  Unlike the situation with blood or semen, the exact bodily source of this touch DNA cannot be determined, however it can be from skin cells, perspiration, etc. It is also important to understand that minute amounts of DNA that have been transferred by touch can now be detected. For example, I could shake your hand and then touch an object and transfer your DNA to the object under certain conditions.

Although no blood was detected on the blade of the knife, a trace amount of DNA consistent with Kercher was obtained.  The techniques and results obtained for the DNA on the blade are hotly contested it would seem.  Apparently the results were rather low-level and partial. It is important to note that the DNA was consumed in the analysis and therefore any independent re-testing is impossible. I am often asked to be present during analyses at crime labs when testing will consume the DNA evidence.  This is a basic right of defendants in the U.S. Apparently, there were several testing attempts made by the analyst to get results from the blade, and testing parameters may have been stretched.  From what I understand about the quality of the results, the statistical significance of the inclusion of Kercher (if even scientifically defensible) should be quite low.  Shockingly, laboratories sometimes will report the inclusion of someone as a possible DNA contributor without offering a statistic that quantifies the association. If the DNA results are partial and low-level, statistics can actually be quite low, such as 1 in 4!

Testing for blood in a crime lab is typically first done by simply visually examining an item for possible stains, often with magnification. Suspected stains are then subjected to presumptive tests for blood which are highly sensitive, but not specific.  A positive finding indicates the possible presence of blood (not necessarily human), however other things can cross react with the test, so it is not a confirmation.  The real value of the test is how sensitive it is.  With a negative result, laboratories can confidently report that not even a minute trace of blood was detected.

It sounds as if there were no visible stains on this knife.  Laboratories may do a general swabbing of a surface just to see if trace blood may be present.  An argument in this case for the absence of blood, is a potential clean up with bleach. It is interesting to note that bleach will result in an inconclusive presumptive test result for blood when using a test such as TMB, which I understand was used in this case.  If in fact an inconclusive result for blood was not obtained during TMB testing for blood, it may suggest that traces of bleach are not present.  It is also not clear how a clean up theory explains the blood traces being removed, but not DNA traces.  Since the presumptive testing for blood is rather sensitive, any DNA detected can positively not be associated with coming from blood.  Blood contains a high level of DNA.  As to whether some cellular material from the blood somehow survived a bleach cleaning, well….I suppose its not impossible, but there any many other explanations for the presence of DNA in this instance. Certainly when DNA results are extremely low-level and obtained by potentially too-aggressive typing methods, the interpretation of their significance is practically impossible.  Contamination also has to be considered in these instances.

Bra Clasp


Apparently the bra clasp was not collected until 47 days after the incident.  Immediately, there are questions about the integrity of this evidence.  This is particularly true since crime scene documentation is said to show the clasp at different locations inferring that it had been moved around during the investigation.  As with the knife, there is no possibility of a second, independent DNA test due to consumption of sample and issues with its preservation.

DNA testing of the clasp apparently indicated a mixture of DNA with Kercher the likely major contributor, and Sollecito not being excluded as a minor contributor.  Once again, we do not know the statistical significance of Sollecito’s inclusion, but mixtures are more difficult to interpret and the statistical significance of the inclusion of minor contributors is often quite low.  Even if it is assumed that there is a low level of Sollecito’s DNA present on the clasp, what does it prove? There is no way to determine when or how the DNA was deposited.


 In order for the DNA experts in this case to fully vet the conclusions, results, procedures and interpretations reached, there are several items of discovery that are needed.  DNA testing reports themselves actually tell very little about the testing.  Typically, there are hundreds of pages of notes, data, photographs, etc. that are critical in determining the analyst’s approach, any issues with quality, the true nature of the evidence, and whether protocols were appropriate.  The actual DNA testing produces raw, electronic data that another analyst can use to independently interpret the DNA typing data.  The laboratory’s specific protocols and interpretation guidelines are necessary for a reviewer to determine if conclusions made in a report are warranted, and what shortcomings they may have. It is also important to obtain the quality record of the laboratory and the analyst to determine the prevalence of mistakes, contamination, etc.

Based on recent news reports, the defense DNA experts in the Knox case have not been provided with the materials they require to conduct a thorough review of the DNA typing. I routinely find myself fighting battles to obtain complete discovery in DNA cases that I review in the U.S.  With the stakes so high, the defense absolutely has a right to perform their due diligence.

In closing, I hope that this post provides a general understanding of the issues surrounding DNA cases and the intricacy of the analysis and interpretation.  Forensic DNA testing is not akin to clinical testing in which ‘yes/no’ or ‘positive/negative’ results are always obtained.  While the technology of DNA testing has advanced remarkably in its short history, the increased sensitivity presents interpretation challenges. It can be at times ‘too sensitive for its own good’.  It is interesting to note that the ability to pinpoint exact bodily sources of DNA has not kept pace with DNA testing advances.  Human blood and semen can be positively identified, testing can strongly suggest the presence of saliva, but other body fluids simply cannot be positively identified.

I recently attended an interesting presentation by Donald Johnson at the California Association of Criminalists DNA workshop that dealt with characterizing bodily source of blood stains.  For example, is victim blood at a suspect’s house from an innocent finger cut, or does it contain molecular markers that illustrate that the blood came as a result from a gunshot to the head, and thus contains trace brain material?  These are exciting advances that will hopefully make forensic DNA evidence easier to interpret.

Note:  as I am completing this blog post, I have received more specific DNA information on the case and look forward to reviewing it and potentially offering a more specific opinion.

 Web resources:







  1. I have been blogging on the DNA forensics of this case for well over a year at viewfromwilmington.blogspot.com. I look forward to future conversations with you, especially about the mixed DNA.

  2. Chris, we have been reading your insightful posts and appreciate them, I invited the current blogger to chime in to get additional outside insight onto the dna issues, thanks.

  3. Thanks Doug. That is definitely a limitation with DNA analysis. There is no real way to determine when it was deposited. DNA is found within white blood cells in the blood and is a rich source of DNA. Certainly you would expect to find a fair amount of blood on a murder weapon. The finding of a trace amount of DNA is not particularly consistent with blood, since even tiny blood specks can provide full DNA profiles.

  4. Doug, The idea (in Darkness Descending) that strong peaks in the electropherogram mean that a sample comes from blood is dangerous nonsense. Colonel Garofano is trying to make a DNA profile into a kind of test for blood, and it is no such thing.

  5. Anonymous commenter The Machine asked about Luciano Garofano’s words in the book Darkness Descending at PMF. Here are the quotes: “However, here is the electropherogram and you can see that the RFU value is very high, so the sample is undoubtedly blood, which is the body fluid that provides the greatest amount of DNA. In some cases you see higher peaks of Amanda’s DNA than Meredith’s. Amanda has been bleeding. Nor is it old blood, as the defence might say, because blood decays fast. We have the same result on the cotton-bud box. The light switch was over-scrubbed, but from the film the way the cotton-bud was good enough. There too we have mixed blood. So that’s pretty significant for Amanda, Unfortunately for her, she bled at the same time Meredith was bleeding. That’s a lot to explain” (Darkness Descending, page 371).

    “Look, ten out of sixteen loci have peaks that correspond to Amanda’s DNA profile. The hypothesis is that Amanda also touched the bra clasp”

    “My conclusion is that the bra clasp certainly works as a piece of evidence – it is a strong clue against the suspects Amanda and Raffaele. The RFU number is high enough. So the result is perfect.” (Darkness Descending, page 379).”

    These passages are pure drivel. (1) The size of the peaks (their RFU values) cannot be related to tissue-type, as Greg Hampikian told Charlie Wilkes, at the IIP forum, IIRC, and also on the first Amanda Knox continuation thread at JREF. Consider Meredith’s peaks on the clasp, as just one of many examples in which the peaks are strong but there is no blood. The cigarette butt may be even a better example of a piece of evidence with strong peaks but no blood. (2) Garofano is trying to claim that the lack of degradation means that it is a fresh sample. In general, the rates of decay of DNA depend upon so many factors that one cannot say when the DNA was deposited. (3) I have looked at the electropherogram myself, and I see a small number of extra peaks in a few loci. Anyone who claims that there are ten loci out of sixteen that have Amanda’s DNA is a knave or a fool.

  6. Great question. This is an interpretation limitation of forensic biology. In order to confirm that an apparent bloodstain is human blood, the identifying feature that must be identified is human hemoglobin. Everyone’s human hemoglobin gives the same type of test result…positive. So, if a drop of blood contains blood from 1 contributor, or multiple contributors,the human hemoglobin test result is the same…positive.

    If DNA testing of a stain identified as human blood is conducted and a single DNA profile is detected, then it is fair to conclude that the DNA is from the human blood since we know that human blood is rich in DNA. There is actually some debate in the forensic community about how far you need to go in identifying human blood itself. Some feel that if it looks like blood, gives a positive presumptive test for blood, contains an amount of DNA consistent with human blood, and DNA typing results are obtained, it proves that human blood is present. However, in a hypothetical scenario in which, say dog blood is deposited over an invisible stain that contains human DNA (e.g. heavy concentration of perspiration or saliva), this analysis scheme would indicate that the DNA is from human blood, even though that is not the case. Certainly laboratories must perform confirmatory tests on drugs in order to report their presence with confidence, why should it be different for human blood? Logical inferences must be couched with the proper language identifying them as such in reports and testimony.

    If a stain that is identified to contain human blood contains a mixture of DNA from multiple individuals, there is no way to positively determine if in fact there were multiple bleeders. A DNA result looks the same for any type of cellular material. A principle that can be used to frame possible interpretations is that we know that blood has a high level of DNA in it. So, if there is an apparent mixture of two individuals, and one of the individuals is present at a very high level while the other one is minute, there are at least two possible explanations (neither of which are necessarily more likely). 1: There is a lot of blood from one person mixed with a small amount of blood from a second person or 2: The major DNA donor was bleeding and the blood was deposited on an area that contained a trace DNA component from a second individual (e.g. saliva, perspiration, touch DNA). Another issue is that there is no way to determine if both sources of DNA were deposited in/on the stain at the same time.

    As you can see there are a great number of considerations and alternate interpretations here, and I’m sure I could have hit on more scenarios. This is a great example of DNA testing technology being more advanced than body fluid identification. Other clues at the crime scene such as blood stain pattern interpretations can potentially assist in these types of DNA interpretations. The bottom line is that there is limitation to the science here.

  7. I would say that presumptive tests for blood are often based on the pseudoperoxidase activity of hemoglobin. However, there are false positives, and a presumptive test should be followed by a confirmatory test. Confirmatory tests sometimes use other biochemical markers, distinct from hemoglobin. There is a good review article on the testing of body fluids from about 2009 in Forensic Science International. The coauthors are Virkler and Lednev.

  8. Have you only reviewed information received from the innocence side? I see your links are to websites convinced of innocence and your analysis based on information received from them.
    Have you reviewed any information from the prosecution as well?

  9. Helena,

    Thank you for weighing in. That is a great point and you are correct, the sites that I mention are indeed from one point of view. I however would only consider facts to be the actual DNA data, which I have not yet reviewed. My studies on the case to date have been merely to get an idea of the evidence, and the real intention of my blog is to shed light on possible issues in this case and in fact in any case. That being said, there does appear to be some issues with the DNA in the case.

  10. Helena,

    Virkler and Lednev have no relation to the Knox/Sollecito case. I read the sections of Darkness Descending that concern the forensics, and some of my thoughts are given above. I also read the sections of the Massei report that concern the DNA and luminol-related forensics. I have given an argument elsewhere to the effect that Judge Massei violated a fundamental principle of forensic genetics with respect to Raffaele’s putative profile on the clasp. That does not mean that Raffaele’s DNA is not on the clasp; it just means that Judge Massei doesn’t understand DNA profiling particularly well.

  11. If the investigators had collected all the knives from Raffaele’s kitchen drawer (highly laughable that a murder weapon was being used for food preparation and the investigators could simply pick the right one) and tested them with the same ‘carefulness’ they would have probably found similar results on some others as well. Particles substantially bigger than a picogram keep floating all the time even in air, let alone getting transferred through contact. Imagine what would ave happened to Lumumba if he did not have an air-tight alibi. They would have surely found tons of similar ‘evidence’ from his residence.

  12. Az,

    Thanks for checking out the blog. You are right on with regards to other knifes. Others have suggested that the other knives should have been tested as a sort of control sample to check for ‘background DNA’. While I’m not so sure about the floating DNA theory, the sensitivity of DNA testing means that many household items will have trace amounts of DNA on them. Context is always important in forensic science. How can they justify selection of that particular knife?

    1. Existence of airborne DNA is not a theory but a fact. Body fluids contain DNA and hence when we cough or sneeze we release tiny droplets which can remain airborne at least for some time and could be trasported some distance through breeze. The tiny skin cells that we keep shedding could also do the same. Examining our skin under a stereo microscope, even at a low magnification of up to 40X, will reveal as to how tiny skin cells are ever ready to leave our body. Since I myself use optical and electron microscopes for forensic investigations of a different kind, I am telling this from personal experience. Especially when we are talking about tiny amounts of DNA, not only invisible to the naked eye but also insufficient to render them unavaialble for a retest, numerous possibilities of their transportaion and presence exist. Amanda, being a common factor between Rafaelle and Meredith, can easily trasfer their DNA from one place to the other. For example, if Amanda touches a door knob with Rafaelle’s DNA on her hand and Meredith subsequently touches the same knob and soon after changes her bra then Rafaelle’s DNA could reach Merdeith’s bra strap. I mean the possibilities are endless. Let me ask a simple question here. Why are we splitting our hair and presenting such diverse views on the DNA of Amanda and Rafaelle and not that of Guede. The answer is because the presence of Guede’s DNA is sufficient and convincing enough to secure a conviction but the same is not the case with the other two. Copious amounts of Guede’s faeces and semen could not have been transported by somebody else but the tiny amounts of the DNA of the other two could have easily been. One needs to have evidence “beyond any reasonable doubt” (which exists only against Guede till date) to ensure that innocents are not punished. I am really surprised how prosecution could secure conviction of the other two based on such flimsy evidence and concocted theories.

      The highly unlikely ‘sex orgy’ theory remained unchanged even when Guede turned out to be the culprit and not Lumumba. Was the prosecution saying that Meredith was of such a loose character that she would have readily agreed for sex with any Tom, Dick and Harry or the other two were so wanting in rational thinking that they approached her with a proposal that could have only been turned down? However, Mrignini has called Amanda an intelligent girl in one of his interviews (to CNN, I think).

      As if this concocted theory was not enough to disbelieve the prosecution, a single knife among many in Rafaelle’s klitchen (of all the places) was picked up that was later said to contain Amanda’s DNA on the handle and Meredith’s on the blade (not to mention Rafaelle’s DNA on the mishandled and contaminated bra strap). Give me a break. An attempt at forming public opinion (and that of the un-sequestered judges) in favour of the prosecution theory is too obvious to me. I am convinced that a careful examination would have shown DNA evidence of the involved people at several locations of many knives because contamination is the most likely way the DNA could have got there in the first place. However the prosecution was clearly content at having evidence just sufficient to manipulate opinion.

      Thus the entire case wass based on concocted theories, flimsy evidence and unreliable witnesses. The wrong done to a good girl like Meredith cannot be undone by punishing other innocents just to safeguard the ego of the prosecution team.

      Amanda did tell some lies but many of us do that when we are under pressure to get out of an impending undue problem. Even if one tells a lie under duress in custody it is necessary to correct it at the first opportunity in the court. Otherwise due punishment becomes imperative. Implicating innocent people like Lumumba is particularly unpardonable. However, the time already spent in jail is much more than adequate punishment.

      1. AZ:

        Thank you for your analysis. The DNA of Guede indicating sexual penetration was not determined to be Sperm. You might be interested to know that there was in fact a large apparent semen stain on a pillow case underneath the victim that has never been tested. The Massei report talks about this as has former FBI agent Steve Moore. It probably belonged to Giacomo Slienzi who had had sexual relations with Meredith but there is still no explanation for not testing something like this.

        I am interested in you theories about transfer by innocent means of DNA from a doorknob to the bra clasp. That is always what I thought happened. I’d like to see the defense produce a video of a repeatable experiment demonstrating that DNA from a male hand that touches a door knob can make it to a bra clasp via a female hand that has touched both the bra clasp and the door knob.

        The other point you might consider is that the trial record cannot be published to the internet as it can be in other democracies. Much of the important public debate about the case has been based on internet blog hearsay.

        Please come visit us at injusticinperugia.org

  13. Greetings from Australia,

    As a media (court) reporter from the past I was fascinated by the offer of “discussion of issues surrounding DNA testing”. I followed up the blog posts and read the court story. If I have it right, then Diya Lumumba was freed, not because of a recantation from Ms Knox, but because of the DNA and forensics undertaken by the Italian authorities (and the subsequent arrest of Mr Guede). It is this same Italian forensics team that is criticised for its work on the same crime scene. I read:

    Sentence Of The Court Of Assizes Of Perugia (Presided Over By Dr. Giancarlo Massei) In The Murder Of Meredith Kercher

    I am not sure that the lay person would gain anything from looking at the science of mixed traces of DNA in this case. The Defence says that they can be explained by co-habitation. The Prosecution says the opposite. I provide a short quote from the report:

    “it should be recalled that Amanda Knox, in the course of her own examination (questioning), declared that when she left the house on Via della Pergola on the afternoon of November 1st, the bathroom was clean. It should then be highlighted that in that same bathroom various trace specimens were found, of a mixed nature and testing positively for blood. It is true that, according to what was asserted and explained, it is not possible with a mixed trace specimen that tested positive for human blood to determine which of the trace’s contributors the blood belongs to. In this case, however, non-mixed traces were also found, which were shown to be of a haematological nature [i.e. blood] and turn out to have the biological profile of the victim. Such traces, in particular the dribble of blood left on the right inside edge of the door and the stains left on the light switch (see photographic illustrations 141, 142; 158, 159) lead to the deduction that whoever entered that bathroom had his or her hands covered in Meredith’s blood.”

    From memory, Mr. Guede had shoes on and went straight out the door.


    1. Mark:

      Welcome to the Amanda Knox case. Patrick Lumumba was released because he had an airtight alibi. There was also no forensic evidence of him at the cottage.

      In a hand written statement to police made only hours after her signing another statement prepared for her by police in Italian — which she did not speak at the time — she says clearly that she is not at all sure about anything she said in the interrogation.

    2. Mark:

      You seem to be giving more credit to the forensic team in catching Guede than they deserve. He was a known criminal and had his full DNA record with the police. Therefore, when he left his tell-tale marks (including poo in the unflushed toilet that only he could have left rather than someone transferring it) at the crime scene, where he was least expected to be present, it was synonymous with leaving his Driving Licence at the crime scene. He also ran away from the country soon after the murder. Now you do not have to be a Sherlock Holmes to suspect/catch him. In my view a good forensic team is one that has the required knowledge and facilities and performs its duties diligently without any fear or favour.

      1. In fact if the authorities had not jumped the gun before Guede’s DNA from the crime scene had been analysed and identified, it would have been an open-and-shut case. Neither the other two would have been arrested nor we would have come to know of this case.

  14. Mark,

    IMO the most likely scenario is that Guede went into the bathroom to clean up, then returned to Meredith’s room, then went out the door. What Massei has done is to attempt to put a time stamp on Amanda’s DNA in her own bathroom by misusing Amanda’s words that the bathroom was clean when she left (Amanda probably meant that the bathroom was not bloody). Massei then goes on to say that Amanda deposited her own DNA in the mixed traces when she washed up after the killing. A bathroom that appears clean to the naked eye need not be a DNA-free bathroom. Moreover, there is the problem of the team’s swabbing all the way to the drain plug of the bidet and other collection errors that would raise the possibility of getting mixed DNA.

  15. Joseph, I think many expect the possible semen stain to be Rudy’s because Meredith’s downstairs boyfriend was out of town for several days due to the Nov. 01 holiday 4 day weekend. The expert found smearing of the substance in Rudy’s shoe print indicating it was likely left on the pillowcase under her buttocks in the crime.

  16. Just a small correction for Mark. My understanding is that Lumumba was freed because a customer returned from Switzerland to confirm his alibi because the police would not accept alibis from local people. Amanda was banged up in solitary from the time of the ‘confession’ and was not even allowed a lawyer until the time when she first went before a judge to have bail refused, so although she recanted her forced confession the same morning, the police were not prepared to accept this because they believed Lumumba was involved. They had misinterpreted a text message and set off on a mission to extract his name from Amanda. I have never heard of any mention of Lumumba’s DNA and it is unlikely that any would be found since he never visited the flat.

  17. Since we have discussed testing the possible semen stain for DNA, let me ask if stored correctly how long can testing be done on a semen stain if it is on that pillowcase. They have not shown a good record for testing and stored the bra clasp in a bag with water or moisture which completely destroyed it. How prone is a semen stain to losing it’s ability to be tested, for good results to exist, and is time a factor, is moisture an issue, how should it be stored to insure it will last until the case is over?

  18. David,

    Great questions. Heat and moisture are the number one enemies of DNA because they promote bacterial growth which degrades the DNA. If the semen stain contains spermatozoa, then it will be very rich in DNA. So, even if some degradation occurs in a sample rich in DNA, it will likely be testable for many years. Biological fluid stains should be allowed to dry completely, packaged in paper containers (e.g. manila envelope, paper bag) and kept frozen for optimal preservation. Items with a large amount of DNA such as good sized blood and semen stains will remain testable for many years even if they are packaged when dried and stored even at room temperature.

    When I performed DNA testing I used dried samples of my blood as control samples. These dried stains were kept at room temperature and were testable for years with mild degradation only noticeable after a few years.

    Obviously, the less DNA present in a biological sample, the greater care that must be taken to preserve it.

    Degradation of DNA creates a situation where some or all of the typing information in the DNA is lost. It of course does not change the DNA types of the sample, but can make the results more difficult to interpret.

  19. I certainly don’t think we should rule out the possibility of deliberate malfeasance on the part of the police. It has happened in some of the best labs in the U.S. and it certainly could happen in Italy. Many things make me suspicious–none more than what looks like the deliberate destruction of the bra clasp to prevent retesting. (Who would store valuable evidence in a bag with water?). I also find it highly suspicious that the police have gone to abnormal lengths to avoid giving the defense all of the files and reports they have requested and are entitled to. It is not at all clear that everything has been turned over even now.

    Although the police have not admitted as much, I believe that they selected the knife in question because they were reasonably certain they would find Amanda’s DNA on it. But note what crazy things you have to believe in order to be convinced that this is the murder weapon:

    1) You have to believe that Knox and Sollecito would have kept the knife while going to enormous lengths to get rid of other incriminating evidence;

    2) You would have to believe that they kept–and perhaps used the knife–as kind of a trophy, a daily reminder of how much fun it had been to kill.

    There is nothing at all in the background of either defendant to make me think it is remotely possible that they were guilty of this kind of depravity. Nick Pisa, a journalist who early in the trial was quite harsh on Knox and Sollecito, now says that the case against them is “disintegrating.” He is entirely right.

    1. Paul:

      You have hit the bull’s eye. My guess is that your thoughts have crossed most of our minds as well but we have just stopped short of saying so because it would be very difficult for the defence to tread this path unless they have sufficient evidence from the present case or past cases to at least create a doubt in judges’ minds if not prove it. Otherwise they might just annoy the judges.

  20. The appeals judge, Hellman, has just set hearing dates in mid June for the testimony of 5 inmates who include at least one who claims Rudy masturbated in the killing room. Judge Hellman has been asked by the defense to order the semen stain finally be tested, and after this apparent testimony, he might. We shall have to see if the stain is semen, and if it is still reliable for testing. It sounds like the authorities would look very foolish at this point if they let this possible semen stain become destroyed.

    1. David:

      The prosecution probably already knows that the semen stain does not belong to Rafaelle so do not be surprised to hear “evidence destroyed” yet again. However, if the stain really turns out to be Rafaelle’s, after a retest by an independent laboratory, then I will have to go back to the university again.

  21. Joseph:

    In my view the experiments you have in mind are worth trying if someone has the time and resources. Different modes of transfer that could be tried are those that contaminate the hand with perspiration, skin cells arising from rubbing/scratching, tiny droplets arising from coughing and sneezing into the hand, and perhaps semen if that is relevant to the present case. If the experiments are found to be repeatable then that should be the clincher but even otherwise it should make a reasonable case for other possibilities of transfer than the one that the prosecution had the judges believe.

  22. AZ:

    The number of variables are endless. How long since the hands were last washed? Were the hands rubbed together as sometimes happens with cold weather? You get the point. I don’t work with forensics so I would really like to know what the experts know. I am very frustrated with the public’s lack of access to the trial record.

    As you might know if you have followed the case, there was talk of the DNA of other people on the bra clasp. I would like to know more about that.

    The bottom line with the case is that the DNA evidence is overrated. Dubious forensic evidence must be balanced against social factors that all but exclude the participation of Amanda Knox and Raffaele Sollecito.

  23. Joseph:

    There are so many apparent flaws in the case that the defence should have won it hands down but they lost it. If the bra clasp had DNA of other people, which could not be matched with any of the people involved, then the defence should have made a strong point that a bra clasp can sometimes have DNA of people who have not touched it, which clearly suggests other means of transfer. The strict guidelines for collecting DNA samples also imply the same. The list dubious evidence and interpretations goes on and on but the judges were not convinced of any of the defence arguments even to give the benefit of doubt to the accused let alone finding them innocent. I am not sure what more they knew that we are not aware of.

    Amanda’s own behaviour and approach did not help the cause either. She does not make things clear in her own note, which was probably written under no pressure. I would have liked to read “how can the police have any proof when I was not there” but she says “I don’t know what proof they are talking about, but if this is true, it means I am very confused and my dreams must be real”. If she is a fair-minded lady she should never have accused Lumumba (or at least retracted the statement at the first opportunity) irrespective of what happens to her. None of which proves her to be a murderer though, except in Judges’ mind that matters the most. This case clearly gives a lesson to all the accused innocents that if they do not persist with the truth then they will be subjecting themselves to manipulation.

    I know that exact replication of what might have happened is difficult but I doubt if the system there relies heavily on any rational approach. One has to somehow convince the judges a la Mignini.

  24. The following links provide interesting insights into innocent transfer of DNA, which took me less than a minute to find on the internet. A thorough search might yield much more authentic sources that are respected internationally.



    At the least, the defence team should look for some authentic published sources and/or bring some renowned experts to the court in order to discredit the prosecution’s ‘crucial DNA evidence’ claim.

  25. It also goes without saying that the extreme measures good DNA labs take to prevent cross contamination of evidence or contaminating evidence with their own DNA, illustrates the point that innocent transfer of DNA is something to consider. I wonder if the defense team asked for (or was provided with) logs of contamination events within the lab on other cases.

  26. The defense did not receive electronic data files or machine logs. From what I can gather, they received no information on negative controls. I am not aware that Dr. Stefanoni’s lab had or did not have a contamination log. She made the claim that she was unaware of any contamination event in seven years in the lab.

    The defense team used Sarah Gino and Adriano Tagliabracci as their expert witnesses at the first trial. They wanted more expert witnesses as the appeals trial, but the judge instead went with independent experts. The defense team did get to introduce a short letter in the appeals trial from a world-renowned DNA expert.

    1. Chris:

      The judges’ decision to go with independent experts cannot really be faulted. In fact, I would have done the same in their place because the defense team would always bring witnesses favorable to them (though witnesses of high repute should largely nullify that factor). If I was in the defense team I would have also tried to produce a reputable journal paper or book, that was preferably published before the date of the murder, in order to completely eliminate any suspicion of possible bias. Nevertheless, I sincerely hope that judges will make better use of their common sense this time even though they have to unfortunately continue to rely heavily on expert witnesses for crucial matters of the case.

  27. If a forensic DNA lab states that it has not seen contamination in its lab….that very likely means that they are not looking hard enough. Contamination is inevitable on some level in DNA labs.

  28. Some people might have found this blog rather one-sided earlier but the court-appointed DNA experts’ finding that the DNA evidence is unreliable clearly vindicates the view expressed here.

  29. Independent lab report translated:

    ITEM 36 (KNIFE)

    Relative to the genetic analysis performed on trace A (handle of the knife), we agree with the conclusion reached by the Technical Consultant regarding the attribution of the genetic profile obtained from these samples to Amanda Marie Knox.

    Relative to trace B (blade of the knife) we find that the technical analyses performed are not reliable for the following reasons:

    1. There does not exist evidence which scientifically confirms that trace B (blade of knife) is the product of blood.

    2. The electrophoretic profiles exhibited reveal that the sample indicated by the letter B (blade of knife) was a Low Copy Number (LCN) sample, and, as such, all of the precautions indicated by the international scientific community should have been applied.

    3. Taking into account that none of the recommendations of the international scientific community relative to the treatment of Low Copy Number (LCN) samples were followed, we do not accept the conclusions regarding the certain attribution of the profile found on trace B (blade of knife) to the victim Meredith Susanna Cara Kercher, since the genetic profile, as obtained, appears unreliable insofar as it is not supported by scientifically validated analysis;

    4. International protocols of inspection, collection, and sampling were not followed;

    5. It cannot be ruled out that the result obtained from sample B (blade of knife) derives from contamination in some phase of the collection and/or handling and/or analyses performed.


    Relative to Item 165B (bra clasps), we find that the technical analysis is not reliable for the following reasons:

    1. There does not exist evidence which scientifically confirms the presence of supposed flaking cells on the item;

    2. There was an erroneous interpretation of the electrophoretic profile of the autosomic STRs;

    3. There was an erroneous interpretation of the electrophoretic profile relative to the Y chromosome;

    4. The international protocols for inspection, collection, and sampling of the item were not followed;

    5. It cannot be ruled out that the results obtained derive from environmental contamination and/or contamination in some phase of the collection and/or handling of the item.


    Prof. Carla Vecchiotti

    Prof. Stefano Conti

  30. Pingback: Michelle Malkin | » Forensic nightmare: The perils of touch DNA

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