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False positives common in drug field tests; the innocent at risk

Matthew C. was charged with possessing 92 grams of heroin after a baggie full of white powder was discovered in his van. The powder allegedly tested positive for heroin in a field test. In reality, it was laundry detergent.

Matthew was innocent but was charged with crimes that could lead to 15 years in prison. His bail was set at $500,000, an amount he couldn't possibly afford. Even his family doubted him. He spent 41 days in jail awaiting the official lab results that would exonerate him.

Matthew was released after it was discovered that the arresting officer had been turning in a lot of false positive test results. It looks as if he simply lied about the results. As many as 80 cases are under review and may be tossed out. The officer has been fired and may be criminally charged with false arrest.

Drug field tests are known to be inaccurate

According to a 2016 report by ProPublica and the New York Times Magazine, American police arrest an estimated 1.2 million people each year for drug possession. In most of those cases, the arrest is justified by a field test.

Yet field tests are so notoriously inaccurate that both the National Bureau of Standards and the Justice Department have warned that they should never be used as the sole evidence in drug cases. In fact, field tests are inadmissible in virtually every U.S. jurisdiction.

The tests, which have changed little since the 1970s, are known to be problematic. One Florida study found, for example, that 21 percent of substances police identified as methamphetamine were not. Further, of those misidentified substances, half weren't illegal. Nevertheless, the field tests undoubtedly resulted in arrests.

There is no agency tasked with regulating the tests or how they are to be administered. Yet heat, cold and even lighting can affect their accuracy. Police officers may receive little training on how to perform the tests, and they can -- and do -- make mistakes.

What is the harm done by relying on questionable field tests? After all, only a lab test can be admitted as evidence. Doesn't that mean that no one can be convicted on the basis of a field test alone?

Unfortunately, that is not the case. The vast majority of U.S. criminal cases are resolved through plea bargaining, and that usually takes place before the lab test results are in.

As we've discussed before, there is tremendous pressure to plead guilty, especially when someone is being held in jail because they can't afford bail. Moreover, even if the case is later dismissed when a lab test determines the substance is not illegal, as Matthew C.'s case illustrates, people can sit in jail for a long in time before that happens. They may have lost jobs, become estranged from their own family, or lost custody or visitation with children due to the false allegations. 

It simply is not justice for people to be jailed or convicted based on field tests known to be unreliable.

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