ProPublica’s investigation on unreliable roadside drug tests used to secure guilty pleas across the country is the winner of the John Jay College/Harry Frank Guggenheim Award for Excellence in Criminal Justice Journalism. ProPublica won in the “series” category of the prize, which is administered by the Center on Media, Crime and Justice at John Jay College.

Written by reporters Ryan Gabrielson and Topher Sanders, the series spotlighted how tens of thousands of Americans are jailed each year based on $2 police drug kits known to produce false positives. The first installment, “Busted,” published with the New York Times Magazine, chronicled the wrongful conviction in Houston of Amy Albritton, who had no criminal record when she was jailed because one of these kits, known as chemical field tests. In “Unreliable and Unchallenged,” the reporters uncovered how the Las Vegas police crime lab had for years known that field tests can produce false positives – yet kept using them, never bothering to inform the judges who were handling the city’s drug cases, and its thousands of annual convictions.

This reporting prompted the district attorney’s office in Portland, Ore., to review its drug possession cases. The office discovered five cases where defendants had pled guilty – but subsequent lab tests came back negative for the presence of any controlled substances – and vacated those five wrongful convictions. Portland’s district attorney’s office also changed the way it secured guilty pleas in drug possession cases based on these tests: now such pleas will not stand unless the preliminary police roadside test undergoes a lab analysis to have its results double-checked. In Las Vegas, spurred by ProPublica’s reporting, the Nevada Attorneys for Criminal Justice set up a committee looking for ways to challenge law enforcement’s methods for getting drug convictions.

See a list of all the winners here.