Mixed DNA, Not Mixed Blood

Investigators found the mixed DNA of Meredith and Amanda in a total of six samples among dozens that were taken. Three of these samples were from the bathroom that was shared by Amanda and Meredith. The other two housemates used a different bathroom. Mixed DNA was also found on swabs taken from Amanda's room and a latent shoe print in the hallway. A swab from Filomena's room revealed Meredith's DNA with what appears to be a very weak profile for Amanda.

All of the mixed DNA samples from the bathroom were visible bloodstains. Most likely they were composed of Meredith's blood mixed with an organic residue containing Amanda's DNA. No test was performed to determine if any of these samples contained the blood of both Meredith and Amanda, and there is no evidence that any of them did.

The other three mixed DNA samples were taken from latent stains revealed with luminol. No test was performed to confirm the presence of blood in any of these samples.

The prosecutor has tried to insinuate that these findings are incriminating.  The most plausible explanation is that the mixed DNA is simply a result of cohabitation. As an example for the sake of comparison, investigators used luminol in Raffaele's apartment and found a latent stain with the mixed DNA of him and Amanda. Here is an example that you can relate to in your own home. If you cut your finger and your blood lands on a sink in a bathroom shared by other person in your house, you will get the exact same result. Your DNA will be mixed with the DNA from the other person that also used the bathroom. All it means is that two people have been sharing the same space.

7 comments:

Al-Fakh Yugoudh said...

Sure it's possible!

But in Filomena's bedroom there was a latent footprint which tested positive to the victim's blood and to Amanda Knox's DNA.

Is it possible that a mysterious murderer (or Rudy) might have been barefoot and after the murder gone to Filomena's bedroom and accidentally stepped on a piece of DNA belonging to Amanda, which she might have left there when days earlier she visited Filomena's in her room?

Sure it could be possible.

However the judges believed that it is much more likely that Amanda herself went to that room with bloody feet for the purpose of staging the burglary, and in that process she left some of the victim's blood and her DNA.

It's not always what is possible, but what is likely that sticks in the mind of those who have to decide in court. And that is true in most murder cases.

SomeAlibi said...

The court states that Amanda's DNA are skin cells which came off when she was washing blood off her hands in the sink and off her feet in the bidet. The 'left over' DNA argument - that it was Amanda's skin from her normal use of the flat would seem at first look to be perfectly reasonable but there was no other flat-mate's DNA co-mingled with Meredith's blood. If it had been one or two instances, perhaps you could still go with it. However it is *five* separate areas and in each the court has found it is consistent with someone leaving their skin cells when cleaning blood off. No unexplained DNA was found in Meredith's blood - only Amanda's.

Various areas were then cleaned (per the court) which I have reflected in your post on "no clean up" which is directly contradicted by the court.

Kestrel said...

DNA tests from Raffaele's flat resulted in several mixed profiles of Raffaele and Amanda. Not because one of them murdered the other, but because they were sharing the apartment for a few days.

If we swabbed several spots in your bathroom, we would almost certainly find your DNA mixed with the DNA of anyone else in your household who shares that bathroom.

Meredith and Amanda shared the small bathroom. Filomena and Laura used the larger bathroom. Finding Meredith's and Amanda's DNA mixed in the bathroom they shared is to be expected. If you had tested the room the week before the murder, you would also have found mixed DNA.

In TV crime dramas, DNA is only left during crimes. In the real world, humans shed DNA all the time.

Anonymous said...

"However it is *five* separate areas and in each the court has found it is consistent with someone leaving their skin cells when cleaning blood off."

There's no scientific basis or logical justification for that assertion. Please stop drinking the Kool-Aid and think for yourself. Thanks.

SomeAlibi said...

Anonymous; you've got to come down off your soap-box - what I've explained to you is how the five co-minglings are actually written up in the judge's report.

If the defense can counter that, then of course, that may be the basis of or part of the basis of a successful appeal. But it *is* the finding on the court based on the prosecution forensics which the court found more convincing than the defense. You don't have to agree with that for a second (that's what the appeal's about after all) but simply stating "there is no scientific basis or logical justification" makes it sound like a black and white issue which it isn't.

Again, you don't have to agree, but I'm trying to strip away these absolute assertions which are unhelfpul to the accurate understanding of BOTH sides of the case.

Kate said...

Actually there were at least two instances in the bathroom where low peaks indicated the presence of DNA from other people; from memory, it was the sink and the box of cotton buds.

Amanda and Meredith's mixed DNA in the bathroom they shared is only to be expected. As Kestrel says, Amanda and Raffaele's mixed DNA was found all over his flat. A highly likely source of DNA is hand towels. Anyone who'd dried their hands on the towels in the days leading up to the murder would very probably have left their DNA there; the 'rubbing' action of someone drying their hands is very likely to leave skin cells.

Rudy took those towels into the bedroom, he stepped on them, he handled them. Rinsing his hands under the tap would be unlikely to leave his own skin cells unless he was rubbing them together. Just holding them under the running water wouldn't do it. If any explanation were needed for Amanda's DNA in her own bathroom, which it isn't, the fact Rudy had handled the towels which surely contained her DNA would explain it.

I'm not sure if this is accurate, but I read that the alleged shoe print revealed with luminol contained Amanda and Meredith's DNA. How is this possible? Shoes don't have DNA. If true, the only way that DNA could have got there is either that it was already there when Rudy stepped on it, or that it was tracked there because he stepped on something that contained her DNA.

Anonymous said...

I read that the alleged shoe print revealed with luminol contained Amanda and Meredith's DNA. How is this possible? Shoes don't have DNA. If true, the only way that DNA could have got there is either that it was already there when Rudy stepped on it, or that it was tracked there because he stepped on something that contained her DNA.

--
excellent point.

there was a lot of people tromping around in that cottage before the Dec 18 Luminol work.