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posted by martyb on Tuesday July 26 2016, @12:12PM   Printer-friendly
from the I'm-positive-there-are-false-positives dept.

Pro Publica and The New York Times Magazine have each written about field drug testing by U.S. law enforcement agencies. The tests are undertaken with disposable kits containing chemicals. A sample is brought into contact with the chemicals and there may be a colour change, which is assessed by the officer. The essay tells the story of people against whom criminal charges regarding illegal drugs were filed, with the results of these field testing kits as the primary evidence in the prosecutions.

According to the essay, the use of the kits has various pitfalls which can lead to false positive results. For one thing, analytes which are legal to possess can produce the same colour change as illegal substances. For another, poor lighting which may be encountered in the field can distort the officer's perception of colours. Confirmation bias can occur. Also, officers may receive inadequate (or--the submitter supposes--incorrect) training in the interpretation of the colours. A former Houston police chief offered the opinion that

Officers shouldn't collect and test their own evidence, period. I don't care whether that's cocaine, blood, hair.

The essay mentions gas chromatography–mass spectroscopy (GC-MS), an instrumental method which is typically undertaken in a laboratory, as providing more reliable results. The submitter notes that portable GC-MS equipment does exist (1, 2).

Nationwide, 62 percent of forensics labs do not conduct further testing in cases in which a field drug test was used and the defendant made a guilty plea. However, the Houston crime laboratory has been doing such testing. They have found that false positives are commonplace. The district attorney's office for Harris County, Texas, which handles cases from Houston, has been informed about those test results and is undertaking "efforts to overturn wrongful convictions." In three years, about as many such convictions have been overturned in Harris County as in the rest of the United States.

Referenced stories:


Original Submission

 
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  • (Score: 2) by Beryllium Sphere (r) on Wednesday July 27 2016, @12:19AM

    by Beryllium Sphere (r) (5062) on Wednesday July 27 2016, @12:19AM (#380523)

    Because they're motivated by arrest and conviction numbers and not by scientific accuracy or justice.

    A bogus drug test is a success in a corrupt system if it allows putting someone in jail who can't afford to bail out. The cop gets credit for one more arrest. After the victim realizes the only way to keep their children is a guilty plea, the prosecutor gets credit for another conviction.

    Coerced pleas are absolutely a thing. Imagine being told that you can plead out to time served and get back to your job and kids in time to keep them, or else stay in jail for months until a trial date. Even that assumes you might get a fair trial. The Tulia defendants who pleaded guilty didn't expect to get one. https://en.wikipedia.org/wiki/Tulia,_Texas#1999_drug_arrest_scandal [wikipedia.org]

    System's broken, folks, and it doesn't work like it does on TV.

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