Sunday, February 21, 2010

Farah Jama and forensic DNA contamination

Part VIII in a series on the Knox/Sollecito case

I have previously posted on DNA contamination issues and subsequently used this post as a starting point to examine the bra clasp and knife as evidence in the murder of Meredith Kercher. I would like to give an additional example of DNA contamintion, that of Farah Jama, an Australian convicted of rape. He spent sixteen months in prison before being released (

The twenty year-old Mr. Jama’s DNA profile was found in connection with a possible rape that occurred at a club for those over 28. The woman had no memory of the night. Mr. Jama claimed that he had been reading passages from the Koran to his critically ill father on the evening of the alleged crime. His brother and a friend gave supporting evidence (

According to an article in the Herald-Sun on 7 December 2009, ‘The same forensic officer who conducted the tests on the alleged rape victim had done another unrelated test the day before that involved Mr Jama's DNA.” This is the key point; as we have seen before in other cases, when two samples are run at almost the same time, there exists a real possibility for contamination. Another important take-home message is the need to weigh DNA forensics against other evidence (,,26542662-27197,00.html).


William L. Anderson said...


I only can hope that this valuable work you are doing gets into the hands of the right people. Once again, we see what happens when a good scientist applies his knowledge against people who were able to secure a conviction that was politically popular: the good scientist wins hands down.

As I have said before, this is heroic work.

Anonymous said...

I agree with you that Chris is doing valuable work here. The problem I see is that it is starting to cast doubt on all DNA testing as being reliable in any case. What I would like to see is some real numbers showing what percentage of DNA tests are contaminated, or at least an educated guess along those lines. DNA testing is being used to free people "wrongfully" convicted as well. Should we have similar doubts about these tests?

Looking at the Kercher case in particular, I think it is important that we balance the non DNA evidence against the other more circumstantial evidence. Do Knox and Sollecito have a solid alibi? Is there motive, means, and opportunity? Are their statements credible? Personally, I don't think the jury in this case relied entirely on DNA evidence.


One Spook said...


I don't believe that Chris' post casts doubt on all DNA testing as being reliable in any case.

Note that he wrote "Another important take-home message is the need to weigh DNA forensics against other evidence .."

What Chris is explaining is that DNA evidence is not always, in every case the "smoking gun" many might view it as.

In the Knox case, the DNA evidence is weak on its face AS IS the very circumstantial evidence and the sensational "sex orgy story" the prosecutor fabricated from whole cloth.

When you couple that fairy tale story "evidence" with the very weak DNA evidence as Chris has carefully described, you have a dangerous mixture in the hands of a prosecutor who already has a history of overzealous prosecution.

I believe Chris understands at a much higher level than most of us, and indeed most laymen, both the strengths and weaknesses of DNA evidence.

Accordingly, his views are of significant value in understanding and explaining this case.

One Spook

Chris Halkides said...


Your question deserves a whole post or two. In brief I don’t think that anyone can give a good answer about the frequency for several reasons. From what I can gather, not every lab logs its contamination events, and some argue that a contamination event that is discovered at the time should not count (I disagree).

In addition, negative controls cannot probe every kind of contamination event. It might miss sporadic contamination, and it cannot address contamination at the crime scene. I am beginning to wonder whether we should require other kinds of controls in DNA forensics, analogous to substrate controls.

Those problems aside, I still think that DNA forensic testing is the most scientifically rigorous of the forensic disciplines. It is amazingly useful when done correctly. Dan Krane has coauthored a number of powerpoint presentations at In the one entitled “Evaluating Forensic DNA Evidence,” he notes, “The science of DNA profiling is sound. But, not all of DNA profiling is science.”


Sam Clayton said...


I agree with what you are saying but i would like to just share the words of Mary Gaudron (the first female justice of the High Court of Australia), "We have a very good legal system in Australia; our rights are upheld, it is based on good principles. However, we must realise that it is not foolproof and mistakes are made - showing us where we need to be more careful."

I aggree with what you have said in the fact that DNA evidence should not be a soel prosecuting tool and should merely be a contributor to the overall case. But lets not forget it has been the primary and most successful piecve of prosecuting and defensive evidence in the last 20 years. Mistakes are made just like most things in this world.

Chris Halkides said...


I agree completely. As Dan Krane said, the science of DNA profiling is sound, but not all DNA profiling is sound science.


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