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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:
(Score: 0) by Anonymous Coward on Tuesday July 26 2016, @12:53PM
So apparently Harris County is great if you've been wrongly accused of drug charges, but is a pit of misogyny for rape cases
https://soylentnews.org/article.pl?sid=16/07/25/0238223 [soylentnews.org]
Something screwy here.
(Score: 0) by Anonymous Coward on Tuesday July 26 2016, @01:14PM
The prosecutors, police, and prison guards are all different people. It seems like, at least in this specific place, the prosecutors seem to take their job seriously, the prison guards are a nightmare, and the police are somewhere in the middle.
(Score: 0) by Anonymous Coward on Tuesday July 26 2016, @05:23PM
yeah, you're comparing harris county cops/jail vs houston cops/system. they are very different even though houston is in harris county. Both police orgs are too large to describe universally but in general harris county cops are a bunch of fascists while houston cops are somewhat laid back(for cops).
(Score: 0) by Anonymous Coward on Tuesday July 26 2016, @06:01PM
Uh, no.
In the rape story, the order was handed down from the DA.
The same DA that is at the forefront of overturning false convictions.
Seems odd to me.