Forensic DNA testing has gotten better and better over the years, giving us definitive answers from samples that previously would have been too small or too degraded.
Generally, that has been a good thing. For example, the "wrongly executed" Roger Coleman and the "exonerated" Timothy Hennis were both proved guilty by conclusive DNA matches after the technology improved.
However, DNA testing is now getting so sensitive that it can pick up a person's DNA from a place he has never been or an object he has never touched by transfer from someone else. Ben Knight has this article at Yahoo News.
The problem, of course, is not in the science but in the interpretation. The answer to the rhetorical question of the caption is no. DNA testing cannot be too sensitive, but the results of ultrasensitive tests must be interpreted with great caution.
Generally, that has been a good thing. For example, the "wrongly executed" Roger Coleman and the "exonerated" Timothy Hennis were both proved guilty by conclusive DNA matches after the technology improved.
However, DNA testing is now getting so sensitive that it can pick up a person's DNA from a place he has never been or an object he has never touched by transfer from someone else. Ben Knight has this article at Yahoo News.
The problem, of course, is not in the science but in the interpretation. The answer to the rhetorical question of the caption is no. DNA testing cannot be too sensitive, but the results of ultrasensitive tests must be interpreted with great caution.
It's something of an open secret, at least among forensic professionals, that at its current state, the science of DNA allows us to capture and identify DNA far better than our capacity to determine the probable circumstances of how the source DNA got to where it was found. In other words, physical evidence is more than likely contaminated...by the environment, by those who discovered or collected it, by those who later catalogued and/or analyzed the evidence, or even by those who handled it during courtroom presentations and hearings. Then weeks or years later, without an ability to discriminate by date or location added, we might now collect and at least identify sufficient DNA characteristics to eliminate a guilty person who wasn't a donor to the tested samples, or identify someone completely unrelated to the crime.
Please consider that analysts are only looking at microscopic samples from several locations on a piece of evidence that may contain available specimens covering square inches, or in other words, a very small fraction of what's really there. There is no way to determine if the identified DNA came from the body fluids of an original criminal, or from the hands of the guy who unwrapped the package 5 minutes ago, or from anyone in between who touched the evidence.
This is undoubtedly what is happening in some of the so-called "exonerations" which involved DNA samples from decades old physical evidence.
JCC