Courts in Las Vegas overturned five drug convictions following reporting by ProPublica that detailed flaws in the field tests that police departments across the country have used for decades to make arrests.

The Clark County District Attorney’s Office only disclosed the 2017 wrongful convictions this year to the National Registry of Exonerations, which added them to its national database. The Las Vegas exonerees were convicted of possessing small amounts of cocaine between 2011 and 2013.

Las Vegas officers field tested white powder found with the accused and came to the conclusion it was cocaine. Subsequent laboratory analysis found the powders were not illegal substances at all, Las Vegas Metropolitan Police Department records show. The records do not indicate whether the lab examinations determined what exactly the powder was.

All of the defendants, facing possible jail time, pleaded guilty to drug charges. One of the exonerees was sentenced to eight months, according to the registry. The other four received community service or left the state before sentencing.

The district attorney’s office filed motions to vacate the convictions and dismiss charges in March 2017. The office did not immediately respond to requests for comment.

The district attorney notified the exonerees of the lab results and worked with them to vacate the convictions.

Clark County is at least the third jurisdiction to overturn drug convictions tied to field tests in recent years, and there have been scores of wrongful arrests in every region of the United States. The Las Vegas exonerations come after five overturned drug convictions in Multnomah County, Oregon, and more than 250 in Houston.

In a 2016 series of stories, ProPublica documented law enforcement’s widespread use of unreliable chemical field tests to make arrests and secure convictions. The reporting focused attention on cases in Houston; Hillsborough County, Florida; and Las Vegas.

The tests are cheap — $2 apiece or less — and they are enormously convenient for police. Officers drop suspicious material in a pouch of chemicals and look for changes in colors that might indicate the presence of illegal drugs. The tests were typically used to establish probable cause for an arrest. Courts across the country have routinely barred them from being used as evidence at trial, demanding results confirmed by certified labs.

Over the years, numerous studies have concluded that they are legitimate tools to establish probable cause to make an arrest but do not prove that drugs are present. Courts across the country have repeatedly refused to admit field test results as evidence at trial.

Regardless, defendants, for a variety of reasons, have routinely pleaded guilty before trial based on the chemical kits. Drug evidence from those cases is often destroyed without lab analysis.

Police and prosecutors have long known the tests are vulnerable to error, ProPublica’s reporting found. There’s no way to quantify exactly how many times the field tests were wrong or how many innocent people pleaded guilty based on the inaccurate results, or to assess the damage to their lives.

By 2010, the Las Vegas police department’s crime lab wanted to abandon its kits for methamphetamine and cocaine. In a 2014 report that Las Vegas police submitted to the U.S. Department of Justice under the terms of a federal grant, the lab detailed how the kits produced false positives. Legal substances sometimes create the same colors as illegal drugs.

Officers conducting the tests, lab officials acknowledged, misinterpreted results. New technology was available — and was clearly needed to protect against wrongful convictions. But the department continued to rely on the field tests, and even expanded their use, for several years after.

Kim Murga, the director of the Las Vegas police crime lab, said in 2016 the department was concerned about inaccurate field test results and potential wrongful arrests and convictions. “We don’t turn a blind eye” to the risk of false positives, Murga said. But she acknowledged the lab had not tried to more effectively eliminate errors.

The Las Vegas police department declined to comment on the overturned convictions. A department spokesman said officers continue to use field tests.

The Safariland Group, which produces the brand of tests long used by Las Vegas police and is the largest manufacturer of the test kits, told ProPublica in 2016 that “field tests are specifically not intended to be used as a factor in the decision to prosecute or convict a suspect.”