Low-cost presumptive field tests in the hands of police officers regularly produce false positives that send people to jail on drug charges. A public defender working in Tulsa County said that about once a month she represents defendants arrested after the field tests produced false positives for suspected drug samples seized by police officers.
Police departments equip their officers with these test kits that cost about $2 each. Investigative reporters at multiple media organizations have uncovered a consistent flow of cases arising from false positives. The tests can report that substances like powdered milk, protein whey powder or laundry detergent are cocaine or methamphetamine. A biology professor explained that the tests were unreliable because the reagents used by the tests can react with many substances in the same manner as illegal substances. The officers conducting the tests must also interpret the color that results from the chemical reaction. Bad lighting at an arrest scene could skew these interpretations.
When police arrest someone for suspected drug possession or trafficking based on presumptive field tests, the person might languish in jail if unable to pay bail. The secondary test results from a state laboratory can take weeks or even months to nullify the results of field tests. In the mean time, a defendant might accept a plea deal despite being innocent to resolve the case.
Police and prosecutors typically pursue drug charges aggressively. The representation of a defense attorney might protect someone falsely accused on the basis of a presumptive field test. An attorney might form a defense strategy that attacks questionable evidence and undermines a prosecutor’s ability to gain a conviction.