“Field tests” of forensic evidence a presumptive disaster: inaccuracies prejudice 1000’s

drug testing copy

The genesis of forensic analysis or “testing in the field” probably goes back to…..

Sherlock Holmes 

Criminal sleuthing at a crime scene or during an investigatory “police stop” is a popular topic in the forensic science commercial laboratory R&D industry. Taking the “lab” to the crime is the essence of advertising news releases I’ve been following for years.

Its a very sexy idea for crime fighters.

There are multiple drawbacks. Mostly in the realm of over-enthusiasm by the commercial vendors, naive police departments telling the crime labs what to do, a mind-boggling lack of validity testing and prosecutors who offer plea deals to criminal defendants innocent of any crime. Here’s a recent blurb on a “learn in minutes” field mass spectrometer.

Of course the “latest” in field testing of substances are sold as being accurate in their results but that only part of this story. The context beyond other issues is that presumptive testing (assuming its accuracy) is NOT testing for conclusive proof of guilt. That can take place weeks or months after an arrest within an actual police crime lab already over run with backlogs.  Hence the popularity (in 90% of those indicted in criminal cases) of plea bargains in cases of actual innocence.

This is a case of a man being charged for possessing soap.

Here is Reason Magazine referring to ProPublica’s recent reporting of drug false positives affecting “tens of thousands of cases” involving field testing of suspected substances.

Another report from 2015 on failed field testing “kits.”

Here’s just a few more examples of these trends:

Mobile and very rapid at scene DNA testing. From 2012 saying the FBI is very eager and” the FBI is pushing to get it into the hands of law enforcement agencies as soon as possible.”

Mobile digital data “extraction.”  

Mobile fingerprint “matching.”

False positives using mobile Mass Spec to test for cocaine in hair. 

Gun shot residue (GSR) finding antimony, lead and barium nitrate is nearly perfect technique, according to a FBI newsletter, if a myriad of steps are followed by police lab workers. False positives are clearly looked at in the literature, but gets short shrift in the article. Here’s a chemistry journal article talking about environment and occupations that contain these substances, a simple and cheap laser spectrometer capable for field use and false positives.

DNA false positives. 

False testing results for marijuana. 





About csidds

Dr. Michael Bowers is a long time forensic consultant in the US and international court systems.
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