Initially, Scott discovered a pink liquid known as cobalt thiocynate that turns blue when it comes in contact with cocaine. However, it also turns blue when it comes in contact with other, perfectly legal, substances. In fact, there are over 80 different compounds that could yield a false-positive—including methadone.
After further experimentation, Scott’s final test was three-fold: cobalt thiocyanate to turn the liquid blue, hydrochloric acid to turn the solution pink again, and chloroform which causes separation of the solution into a pink (top) layer and a blue (bottom) one in the presence of cocaine. Scott ultimately declared that his test was highly sensitive and specific and nearly impossible to misinterpret. Thus, police departments responded in droves, purchasing thousands of them.
Problems arise
In 1974, a National Bureau of Standards study cautioned using these tests as sole evidence for identifying a drug. Then, in 1978, the US Department of Justice (DOJ) determined that field tests should not be used for evidentiary purposes, thus resulting in the inadmissibility of these tests at trial in nearly every jurisdiction. The DOJ urged prosecutors to present a confirmatory test using more reliable methods.
In 1975, Duquesne University-Pittsburgh toxicologists documented several false-positives in these tests and also highlighted the possibility of officers sustaining injuries when opening the acid-filled vials.
Usage
Police arrest 1.2 million people each year on drug possession charges based on these $2 tests which have remained largely unchanged since the 1970s and which have been proven to be unreliable. Nevertheless, many jurisdictions across the country. continue to use these field tests to secure guilty pleas. For example, in 2015, the Las Vegas Metropolitan Police Department made 5,000 drug arrests and secured 4,600 convictions based on field test results.
Additionally, according to a 2016 ProPublica investigation, these test kits were central to dozens of wrongful convictions in Houston by either officers misrepresenting the tests’ results or by the tests’ false-positive results. Since 2014, the Harris County District Attorney’s Office has been working hard to rectify the wrongful convictions and no longer accepts guilty pleas for drug possession unless a crime lab verifies the results of a field test. The state of Texas also created a commission in 2015 to research wrongful convictions based on faulty drug tests and to prevent future occurrences.
Future outlook
The demand for these tests continues to be strong, and at least nine different companies manufacture and sell them. In 2000, the DOJ issued guidelines requiring these test kits to contain warning labels including statements recommending comprehensive training as well as a disclaimer that the reagents can provide both false-positive and false-negative results. However, several companies fail to present these warnings on their labels.
With the growing recognition of the fallibility of these tests, many departments now require that any positive findings are confirmed by a crime lab, and the results of field tests alone are prohibited from being the sole evidence in a trial in many states.
