Widespread evidence shows that these tests routinely produce false positives. Why are police departments and prosecutors across the country still using them? ….
…. There are no established error rates for the field tests, in part because their accuracy varies so widely depending on who is using them and how. In Las Vegas, authorities re-examined a sampling of cocaine field tests conducted between 2010 and 2013 and found that 33 percent of them were false positives. Data from the Florida Department of Law Enforcement lab system show that 21 percent of evidence that the police listed as methamphetamine after identifying it was not methamphetamine, and half of those false positives were not any kind of illegal drug at all. In one notable Florida episode, Hillsborough County sheriff’s deputies produced 15 false positives for methamphetamine in the first seven months of 2014. When we examined the department’s records, they showed that officers, faced with somewhat ambiguous directions on the pouches, had simply misunderstood which colors indicated a positive result. ….
…..Most drug cases in the United States are decided well before they reach trial, by the far more informal process of plea bargaining. In 2011, RTI International, a nonprofit research group based in North Carolina, found that prosecutors in nine of 10 jurisdictions it surveyed nationwide accepted guilty pleas based solely on the results of field tests, and in our own reporting, we confirmed that prosecutors or judges accept plea deals on that same basis in Atlanta, Boston, Dallas, Jacksonville, Las Vegas, Los Angeles, Newark, Philadelphia, Phoenix, Salt Lake City, San Diego, Seattle and Tampa. ….