The law loves science. It doesn’t really understand science, and certainly can’t tell valid science from junk, but it loves that it removes the human variable and shifts responsibility off of untrustworthy human sensibilities and onto something irrefutable. We want proof so that nagging sense that we could be wrong will be eliminated, and science gives us that.  All for $2, which is a pretty good deal.

Field testing for narcotics is an improvement over guessing, which was the way it was done before. Not perfect, but certainly better than leaving it up to a cop’s “training and experience.” And so, a test kit was developed that would fall far short of perfect, but better than “it looked like drugs to me.”

The test . . . involves dropping a suspected drug sample into a vial of cobalt thiocyanate, which is supposed to turn blue in the presence of cocaine. But as Gabrielson and Sanders note, “cobalt thiocyanate also turns blue when it is exposed to more than 80 other compounds, including methadone, certain acne medications and several common household cleaners.” That is not the only cause of false positives:

Other tests use three tubes, which the officer can break in a specific order to rule out everything but the drug in question—but if the officer breaks the tubes in the wrong order, that, too, can invalidate the results. The environment can also present problems. Cold weather slows the color development; heat speeds it up, or sometimes prevents a color reaction from taking place at all. Poor lighting on the street—flashing police lights, sun glare, street lamps—often prevents officers from making the fine distinctions that could make the difference between an arrest and a release.

It is hard to say exactly how common false positives are, although a Las Vegas study found that one out of three samples identified as cocaine was in fact something else. In Florida, Gabrielson and Sanders write, “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.” Since field tests are widely used and police arrest more than 1 million people for drug possession every year, even a relatively low error rate could lead to thousands of erroneous arrests each year.

In context, the fact that we’ve moved from untested, cop-assumed, drugs being good enough for an arrest and prosecution (which may involve being held in jail pending the disposition of either the case or the testing) until a serious test of the substance came back from the lab would seem a step forward. Admittedly imperfect, but since it could take weeks, months, for the lab report to come back (and putting aside the independent issue of whether the “real” lab report was accurate or an Annie Dookhan special), at least it offered some chance for an innocent person to get a negative result.

The problem, however, is science. If it was just the cop’s observations, and assuming the drugs were packaged as kilos of cocaine (which was kinda hard to argue against), one could attack the probable cause at arraignment and raise significant doubts, which occasionally prevailed, and at least served to give pause to setting high bail, allowing a defendant to await the outcome of the lab report at home rather than on the Rock.

The absence of a field test meant that there was room to fight. But with a field test, the fight was futile. The test said positive, and until the labs came back, positive it was. Everyone was comfortable with the belief that the test was sufficient to establish probable cause. And if the test was wrong, it would be corrected when the real lab report came in. Whenever that might be.

What happened in the interim, however, exacerbated the first problem with a second problem.

As the authors point out, 90% of jurisdictions will allow prosecutors to accept a guilty plea based on nothing more than highly-unreliable field test results.

Between the arrest and the return of the labs, plea offers were made. These were usually the sweetest deals defendants would get, often with the opportunity to cop to a misdemeanor rather than a felony, which would be the deal after the labs conclusively proved that the substance was narcotics and an indictment was obtained. Once that happened, things only got worse, much worse.

A few systemic factors were at play here. First, lab testing was costly and time consuming. If prosecutors could take a substantial number of drug tests off the table, it freed up the labs to work on only the more serious cases. Second, the wheels of the system would grind to a halt if defendants refused to take pleas. Calendars would explode, lawyers and judges would be overwhelmed, jails would swell. Third, these defendants weren’t awful or dangerous people, so there was no institutional need to be harsh. A conviction was good enough.

So offers were made that would get defendants out of the system well before any lab tested the substance, and defendants took them. By pleading guilty, it “proved” the field test to be correct, and validated the system’s faith in science.

In Houston, something happened that screwed up the deal. In other places, a guilty plea would mean that the substance would never get tested, since there was no need to waste resources by testing something that no longer mattered. In Houston, however, they tested anyway. It was a disaster, as they learned how many people copped a plea when the substance wasn’t illegal. As a result of the New York Times Magazine story, people came out of the woodwork seeking vindication despite their guilty pleas, even if they couldn’t find Houston on a map.

All the guilty pleas based on flawed field tests turned out not to demonstrate the trustworthiness of science, but the lack of trust in the legal system. Innocent people copped out because the incentives to do so were too strong, while their faith in a fair outcome was too weak. The problem wasn’t that the test was cheap, $2 for a person’s life, but that the system sold its trust for quick and dirty convictions at any price.