Newcomers to this blog are advised to begin with the first two posts, Just the Facts, Ma'am and Case Solved, which explain in very general terms why I believe I've solved this case. Some important questions are answered in the following post, Misunderstandings, Misconceptions, Misdirections. After that feel free to browse whatever topics might interest you (see blog archive).

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Sunday, February 9, 2014

The Problem with DNA

In both the Meredith Kercher and JonBenet Ramsey cases, much has hinged on the interpretation of DNA evidence. And many people have made up their minds prematurely based on this evidence. Thus, since some unsourced traces of DNA were found on JonBenet's longjohns, consistent with DNA found mixed with blood from a stain on her panties, this, in the mind of DA Mary Lacy, must be the DNA of JonBenet's attacker, meaning her parents must be innocent. In the Kercher case, traces of Rafaelle Sollecito's DNA, found on Meredith Kercher's bra clasps, convinced the prosecution, along with the most recent panel of judges, that he must have been one of her attackers. The existence of this DNA, plus a trace of Meredith's DNA supposedly found on a knife blade from Sollecito's kitchen have been enough to convince large segments of the public that he must have been involved.

In the mind of the public, there is something almost magical about the ability of a DNA match to absolutely positively link someone to a crime scene. So it's not difficult to understand why even just a very few traces of his DNA on one single fragment of clothing have been enough to convince so many that Sollecito participated in this horrible attack. And since he and Amanda Knox were so closely linked, the assumption has been that she too was involved, despite the fact that no trace of her DNA was found anywhere in the room where Meredith was assaulted.

There is a problem with the DNA evidence in both cases, however. Thanks to more sensitive methods of retrieving and analyzing DNA, developed only in recent years, it is no longer possible to assume that the presence of anyone's DNA on a particular object means that this person had ever been in direct contact with that object. This problem is summarized in a very interesting report, published on the Internet in 2007, the same year Kercher was murdered, of a Study of DNA Transfer, by Marc Taylor. According to Taylor,
The increasing sensitivity of DNA tests has affected the nature of criminal investigations and has created a new class of DNA evidence. Analysts talk of detecting "trace DNA," such as the minute quantities of DNA transferred through skin contact. DNA typing is currently being applied, with varying degrees of success, to samples such as doorbells pressed in home invasion cases, eyeglasses found at a crime scene, handles of knives and other weapons, soda straws, and even single fingerprints. These developments will bring more DNA evidence to court in a wider variety of cases and may well open new lines of defense. A key issue will be the potential for inadvertent transfer of small amounts of DNA from one item to another, a process that could easily incriminate an innocent person. (My emphasis.) . . .
Primary transfer occurs when DNA [is] transferred from a person to an item. Secondary transfer is when the DNA deposited on one item is transferred to a second item. Tertiary transfer is when the DNA on the second item is, in turn, transferred to a third.
While primary and secondary transfer were well understood at the time, the possibility of tertiary transfer was not. In fact, when I posted regarding this possibility at a forum ostensibly devoted to justice for Meredith Kercher (but actually devoted to the demonization of Knox and Sollecito), I was challenged on that score by someone claiming that tertiary transfer had been tested and determined to be impossible. As documented by Taylor's report, that is not the case. Here is his description of the experiment he and a colleague carried out to test precisely this possibility (the references are to the case that prompted the experiment, commissioned by the defendant, Dr. Dirk Greineder):
Forensic scientists Marc Taylor and Elizabeth Johnson, of Technical Associates (an independent laboratory in Ventura, California) simulated the sequence of events posited by the defense theory: a man wiped his face with a towel, then a woman wiped her face with the towel, then gloves and a knife like those used in the murder were rubbed against the woman's face. DNA tests on the gloves and knife revealed a mixture of DNA from the man and woman-exactly what was found in the Greineder case. Taylor was allowed to present his findings to the jury. Although the jury ultimately convicted Greineder (there was other incriminating evidence besides the DNA), the case is a good example of how the amazing sensitivity of contemporary DNA profiling methods facilitate a plausible explanation for what might at first seem to be a damning DNA test result.
In the Kercher case, the defense argued with good reason that the presence of Sollecito's DNA on the bra clasps was due to contamination, as the item in question had been left lying in the room for over 40 days before being tested. The prosecution countered that, while contamination might explain the presence of a policeman's DNA, it cannot explain the presence of Sollecito's, as nothing containing his DNA was thought to have been present in the building during that time. As I see it, the most likely explanation is that Sollecito's DNA, which by the way, could not be associated with any cell and must therefore be regarded as fragmentary trace evidence, was the result of perfectly innocent and easily understandable tertiary transfer.

Knox and Kercher used the same bathroom, which would have made it easy for the DNA of one to be found associated with the other, via secondary transfer. For instance, as in the above experiment, they could have at some point shared the same towel. Sollecito's DNA would of course have been all over Knox, since they were known to be intimate. Thus, some of the DNA transferred to Kercher from Knox may well have been Sollecito's. It's not difficult, in view of the experiment described by Taylor, to see how his DNA could therefore have been transferred first to Knox by direct transfer, then from Knox to Kercher, by secondary transfer, and finally, from Kercher to the clasps on her bra strap, by tertiary transfer.

I find it significant that Sollecito's DNA was found on an item that Kercher regularly touched, since the most likely means of transfer would be via the hands. If the transfer of Sollecito's DNA to the bra clasps had been the result of his touching them directly, then we would expect to find not only his DNA but his skin cells, yet no cells at all were found, just loose DNA. In view of this, the possibility of tertiary transfer seems far more likely than that of direct transfer, meaning that this "evidence" cannot be used to place Sollecito at the scene of the attack even if we discount the possibility of contamination.

Of course, as far as the general public is concerned, the fine distinctions outlined above mean very little. Once it's been established in people's minds, via simplifications disseminated by the media, but also still accepted in certain quarters, by law enforcement personnel, that someone's DNA has been found at the scene of a crime, then for a great many the issue is settled, and that person must be guilty. And by the same token, though with the opposite effect, interestingly enough, the same naive attitude has led many in the public, the media and law enforcement, to assume that JonBenet Ramsey could have been murdered only by some unknown intruder, who will some day be identified when a DNA match is found.

The fact that the traces of DNA found on JonBenet's clothing and in her blood can easily be explained as the result of secondary and/or tertiary transfer, from some innocent source to JonBenet's hands (perhaps when she touched something someone else had touched, or even petted a dog or cat) and from there to her longjohns and panties, is not at all obvious and can all too easily be overlooked. In view of all the many reasons why no intruder could have been present in the Ramsey home that night, coupled with the lack of any match over so many years to any of the millions of DNA samples in the FBI's Codis files, indirect transfer seems by far the most likely explanation.

The problem with DNA is that the methods used to detect it have become so sensitive as to, in many cases, be counter-productive. The danger that some innocent person will be implicated in a crime has become all too real.


  1. From what I've read about the Kercher murder, RS's trace dna was one of a total of 5 dna traces on the bra clasp.

    In the Jonbenet case, IIRC, we have 6 trace dna profiles.

    So in both cases the "answer" must be either that the murder was done by a committee, or all of the samples can be explained by secondary/tertiary transfer.

    The police in Italy should be looking for the other four "accomplices" :-)


    1. I didn't know about the additional 4 profiles, very interesting. So maybe she too, like JonBenet, was attacked by a "small foreign faction" after all.

    2. In the case of the bumbling Italian police transferring Raffaele's DNA to the bra-clasp, tertiary (3rd) transfer contact wouldn't even have been required.

      For example, in the Massei decision it is well documented (many times) that the police testified that they had rarely changed their gloves when collecting evidence:

      MASSEI Page 102:
      "Profazio did not recall the presence of a rug in Meredith’s room and did not see the bra piece with hooks (p. 49). He added that he did not change the gloves for each object he touched and that for every entry he used the same pair of gloves (p. 52)."

      It is well documented that Raffaele had attempted to break down Kercher's door, and while he wasn't strong enough to effect an entry, just by trying Raffaele surely left his DNA all over that door, which opens into Kercher's bedroom.

      All the dirty-fingered cop had to do was touch the door-knob and then touch the bra-clasp - BINGO!

      This article explains how easy it is to unwittingly transfer DNA:

      30 January 2014

      Kercher trial: How does DNA contamination occur?
      [ ]

      "The clasp was handed back and forth. It's the only thing that has DNA consistent with Raffaele and a number of other people, so I think that's probably contamination as well," adds Dr Hampikian.

      To highlight how easily contamination in DNA evidence can occur, Dr Hampikian's team carried out a demonstration.

      They picked up used drink cans wearing clean gloves and then placed a new knife into an evidence bag without changing gloves. The knife was subsequently found to have tiny fragments of traceable DNA which had been transferred from the can.


    3. Yes, thanks Ken, your point is well taken. DNA can easily be transferred which is why it's so important that all evidence be handled strictly according to established protocols, which was NOT the case here.

  2. No your assumption about the bra clasp DNA is wrong. A tertiary transfer or even a secondary transfer would not have resulted in that strong of a DNA profile. It was not a LCN DNA. It had strong luminescence of several hundred to 1000 RFU. It was also mixed with the victim's blood. And, Knox's DNA was also found with 10 of 16 loci matching. Also, Sollecito's DNA was only found on one other location at the crime scene-the cigarette butt he shared with Knox. DNA transfer is not as easy as you assume. Since he was in the apartment that day wouldn't you expect to find his DNA all over the place if it is as easy as you say. In this case the murder was done by Knox. I believe Knox let Guede into the apartment and she and instigated the assault. Then when the victim would not comply (there was no semen found), Guede restrained her while Knox threatened her. When she would still not comply Knox unwittingly stabbed her. I believe Sollecito was only involved mainly in the cover up. I believe he helped stage the break-in (Guede was long gone), move the victim's body and cut off her bra. They cleaned up the room, the hallway and the bathroom but intentionally left evidence of Guede there and repositioned the body (to facilitate their clean-up). Please go to

    1. The DNA tested in the test described above was also not LCN: "Standard phenol/chloroform extraction procedures were used to isolate the DNA." ( page 2) Yet as noted above, the tests yielded clear evidence of tertiary transfer.

      Also, the possibility of primary transfer can't be ruled out either. It's known that Sollecito spent time at Amanda's place and would certainly have had access to the bathrooom(s) prior to the day of the murder. If one of Meredith's bras had been left there, he might have moved it out of the way.

      The bottom line is that any sort of evidence of this kind, i.e., fiber evidence, DNA evidence, even fingerprint evidence means far less when it is associated with someone known to have spent time on the premises prior to the event in question. While such an explanation doesn't mean he is necessarily innocent, it most certainly can't be used to prove he was present at the time and place of the murder. The bra clasps lay in that room for over 40 days and his DNA was still there. So it's not outside the realm of possibility that it could have been on the clasps for many days prior to the murder. As far as its being mixed with the victim's blood, what can that mean? All they found were some isolated DNA molecules. They were not found inside any cell, they were just free floating. There was plenty of blood, so it's not hard to see how some free floating molecules on the bra could have gotten picked up in the blood and mixed in with the victim's DNA.

      As far as Knox's DNA being found, exactly where was it found? From everything I've read from both sides no one has ever suggested that Knox's DNA was found anywhere in Kercher's room.

      You go on to implicate Knox in the murder, even claiming she is the one who murdered the victim. How can you possibly know that? It's a fantasy.

      You say they cleaned up the room, but obviously it wasn't cleaned up very well as signs of Guede's presence were all over the place. How could they have possibly cleaned so selectively and why would they have wanted to be selective anyhow? If they brought cleaning products into the room to clean up then obviously they would have cleaned up everything. Why not? Looks to me like Guede tried to do some cleaning up and then realized it was hopeless so just left.

  3. And sure, you'd expect to have Knox's DNA everywhere at the crime scene, but they barely found any of Knox's DNA in her own ROOM. So either she doesn't shed much (jk), or perhaps there was a cleanup, as some have claimed.

    I don't think Knox was the one who stabbed Kercher. I'm pretty sure it was Guede, but I find it interesting that Kercher had wounds that showed she was being assaulted from both sides, and there was a bloody footprint found in the bathroom that was much too big to be Guede's.

    I think Knox knows more than she's telling.

    And as for the whole "break-in was real" argument, I doubt anyone would have chosen Filomena's window, as it was completely visible from the busy street. A real burglar would have used the balcony, which was hidden from view and much lower to the ground. I read that the cottage has been broken into twice since the murder, and both people used the balcony. Just because something is possible, like a burglar came in through Filomena's window, doesn't mean it's probable.

    1. "And sure, you'd expect to have Knox's DNA everywhere at the crime scene, but they barely found any of Knox's DNA in her own ROOM. So either she doesn't shed much (jk), or perhaps there was a cleanup, as some have claimed."

      That assertion has been challenged. From what I've read, they only tested three places in Knox's room -- and found traces of her DNA in all three. If they had tested elsewhere they probably would have found it there as well. So to claim they ONLY found three instances is extremely misleading. As for the cleanup, there is no way to selectively clean up one person's DNA while leaving that of someone else. It's invisible. Since there is no sign of AK's DNA and only the one very dubious exemplar from Sollecito (see above) -- in contrast to several instances where Guede's DNA was found, not to mention fingerprints, a palm print and bloody footprints, it's inconceivable to me that the prosecution could see such "evidence" as proof of AK or RS's involvement. As for the bloody footprint, I'm sorry but the fact that it can't be identified means just that.

      Regarding the "break-in," if you want to argue that a real burglar would have used the balcony then you must also accept that someone staging a breakin would also have chosen the balcony. So that's not a viable argument for staging. I recall either reading or listening to an interview with an expert on broken glass (wish we had him in the Ramsey case) and he definitely saw signs the breakin was real. But of course there will always be some other expert to testify otherwise.

      What it all amounts to as I see it is a clear case of reasonable doubt. When you get experts on DNA, glass, etc. who cannot agree, then clearly it's a huge stretch to claim you have proof. As I understand it, the second trial resulted in a verdict of innocent, with no need to revert to reasonable doubt in any case. But if you still feel uncertain and still feel that Knox is hiding something, then you might prefer reasonable doubt. There seems to be no way anyone can claim that they have proven AK or RS's guilt beyond reasonable doubt.

  4. I didn't say that they ONLY found three instances of Knox's DNA in her room. I said they barely found any...which was true.

    You're right about not being able to clean up one's own DNA while leaving someone else's.

  5. hi Doc,, while your theory of jdi seems to me to be the only logical answer given the circumstances of what we know, i still surf the net looking for anything on the case i may not have yet found. I have read something from someone who really knew their stuff when it comes to DNA. They spoke very technically about the various types and how they differ, and then ended with the fact that the unknown male DNA found on jonbenet was 12 time higher than that of someone handling garments at manufacturer, therefor unlikely to have come from this source. I think there was also a link as to where they found the info, and this person was just explaining about it on a blog. What do you make of this?

    1. I'm not sure where that person got that information, but as I understand it, the DNA initially found mixed with JonBenet's blood was just some traces mixed with her DNA as well. It took a very sophisticated analysis to put it all together and even then it was fragmentary.

      Your source was correct, however, in concluding it could not have been from someone at the factory sneezing into the panties, but only because some years later matching DNA was found on JBR's longjohns. Lacy concluded that DNA found in two places on her longjohn's AND mixed with her blood meant that this DNA could only have been from her attacker.

      And that's where the problem lies -- not with what might have happened at the panty factory, but with the interpretation of the DNA evidence later found on her longjohn's. And this is why I made a point in the above post of critically thinking about the meaning of this new so-called "touch DNA" evidence.

      The problem is that, until a match is found, we have no way of determining how and also when both the touch DNA and the DNA mixed with her blood got there. It's not true that the presence of the same DNA in three places tells us anything special. Once some DNA gets on someone's fingers, then it can easily be spread to any other part of that person's clothing or body by that person herself. If JonBenet touched someone -- or some thing containing that someone's DNA -- then it could easily have been innocently transferred to her longjohn's and her private parts by JBR herself, simply through touching (i.e., secondary or tertiary transfer). Older methods of DNA collection might have missed tiny traces of that kind, but the newer more sensitive methods are capable of identifying them -- which makes these new methods potentially so misleading.

  6. In the case of JonBenet Ramsey, with the autopsy indicating repeated acts of her being sexually assaulted, if not a family member committing such acts, how was this allegedly hidden from them?
    There were MANY instances of family covering up and destroying evidence. What would stop them , since they had AMPLE time for a good cover-up, from going to the local "make-out" spot and grabbing a soiled condom and intentionally placing the semen to look as if an "outsider" committed this horrific act to go with all the other tampered evidence?
    If this be the case, some unwitting sap later down the road may be matched and charged for this murder, and all they were truly guilty of - was to play sex games with a partner in a seemingly safe manner, in a seemingly safe spot.

    1. No semen was found. The DNA attributed to her attacker was only one of six unidentified DNA samples found either on her body or her clothing, also in trace amounts. If it had been planted there would have been more than trace amounts.

      I don't think it was planted. But I don't think it means very much either, because we all have traces of DNA on us and on our clothing, due to all sorts of perfectly innocent contacts.