Public Servant,

You write, in part:

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The reason polygraph results are generally not admissible as evidence in a court of law is not that it is less than 100%, but rather that it doesn't meet the judicial Daubert standard (or the previous Frye standard) for scientific evidence. See DaubertOnTheWeb.com.

In some cases, DI polygraph results have indeed been a key piece of "evidence" leading to conviction. For example, Floyd Fay was wrongly convicted of murder in Ohio in large part because he failed a stipulated polygraph examination. You'll find his case documented in the 2nd edition of Lykken's A Tremor in the Blood: Uses and Abuses of the Lie Detector. More recently, an inconclusive polygraph outcome and the Kafaesque interrogations that followed led to a navy cryptologist's wrongly being locked up for more than a year in pre-trial confinement before all charges were dropped. See Chapter 2 of The Lie Behind the Lie Detector for documentation of the case of Daniel M. King.

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Yes, I see your point. This issue was a hot one during a cource I recently took on Criminal Procedure & Evidence. I think most in the LE field would agree that it is extremely foolhardy to rely soley on one piece of evidence when investigating a crime. While DNA and possibly even a polygraph (utilizing a GTK) might point in the direction of one suspect, it is very important that other investigative leads are aggressively pursued to ensure that there is other evidence to conclusively link the suspect to the crime. The reliability and accuracy of any procedure and evidence comes into play when we get into the area that you talked about.

I'm sure we'll all agree DNA evidence is extremely accurate, although not 100%. However, like you've pointed out, it cannot tells us whether or not someone committed a crime, only that they were present. So, once you have a positive DNA match, it is important to take into account several other factors. Did the suspect admit to being there prior to finding out the results of the DNA test? Did the suspect provide a reasonable explanation along with that admission? Or did the suspect lie and claim s/he was never there? If the latter most option is the case, now you have to figure out why the suspect lied, (i.e. afraid of getting caught, afraid of being falsely linked with the crime, etc). However, what you do have is conclusive evidence that they were there. There can be no denying that. Now it's time to figure out why they were there, and either investigate deeper or move on to other suspects.

With the polygraph, coming up with a DI chart is not conclusive evidence that they were there, or had anything to do with a crime, since as Saidme showed us, and the Molly Bish case demonstrates, the polygraph does not have an accuracy rate high enough to make that claim. As an interrogation tool, it is probably excellent for getting confessions out of the guilty, but absent a confession, I would not direct any investigation of mine in a certain direction based on the results of a polygraph test.

I'd also like to address the flip side of what you said, which is, a lack of DNA evidence at a crime scene. I would not like to think that LE agencies are relying too heavily on DNA evidence to solve their crimes, even though DNA is extremely valuable in proving certain things. However, police have been solving crimes long before DNA evidence and polygraphs have been around, so a lack of DNA evidence at a crime scene in no way exonerates a suspect from a crime. It probably just means they were either very careful or very lucky. 

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I think the poly is much more dangerous than DNA, because it is not nearly as accurate in establishing a connection to the crime. Like I said, while a DNA match will establish someone was at a crime scene, it will not establish they committed the crime. Certain kinds of DNA evidence are more helpful than others, e.g., skin under fingernails, victim's hair in the trunk of a car, blood on a pant leg or shoe, etc., while others just prove contact with the victim occured, e.g., semen traces found in the victim. 

Both the polygraph and DNA can be misused and detrimental to any investigation when utilized by an incompetent examiner, but I do not believe even a competent examiner can use a polygraph to conclusively link a suspect to a crime.