Investigative reporter Jim Mustian told the exclusive story of a female informant raped twice in an undercover drug sting after her law enforcement handlers left her alone and unmonitored — a case that exposed the perils such informants can face while seeking to “work off” criminal charges in often loosely regulated, secretive arrangements.

Mustian spent weeks interviewing sources and obtaining confidential law enforcement documents after receiving a tip about the incident which took place in the central Louisiana town of Alexandria early last year. What he eventually uncovered was even more gut-wrenching than he could have imagined.

The woman, an addict who agreed to become an informant after she was booked on minor drug charges, was sent into a drug house to buy meth from a dealer with a three-decade-long rap sheet that included charges of aggravated assault. She was not given equipment that would allow her law enforcement handlers to monitor in real time, but she did carry a tiny camera and microphone that passively recorded the man forcing her to perform oral sex on him — twice — in an attack so brazen he stopped at one point to conduct another drug deal.

“It was one of the worst depictions of sexual abuse I have ever seen,” said a local official who viewed the footage and spoke to AP on condition of anonymity. “Just the audio from it is enough to turn your stomach.”

Mustian’s reporting on the case revealed that the sheriff’s office in charge of the sting never considered the possibility that such an attack could happen, didn’t begin providing informants with real-time monitoring equipment until after the alleged rape, continued to charge the woman with minor drug charges despite her cooperation and, amazingly, moved to reduce the rape charges against the dealer accused of attacking her.

“It’s absolutely horrible,” the woman’s attorney, Harold Murry, told Mustian. “She has a drug problem, and I don’t know if she’s going to be able to beat it or not. But when you become a snitch, they keep your drug problem going and then they arrest you for it.”

But Mustian didn’t stop there. He interviewed experts who told him the undercover informant drug stings that happen thousands of times a day across the country are notoriously unregulated, with vast disparities in how they are conducted, and that many agencies lack the resources to properly train officers or monitor informant drug purchases in real time.

After the AP story moved, television station KALB in Alexandria, Louisiana, asked Rapides Parish Sheriff Mark Wood why his office had not said anything previously about the sting and the alleged rape. Wood said, “Crimes like this, we don’t want to make a big deal out of it for the victims. ... We don’t want to hinder any kind of prosecution.”

As for how Mustian got word of the case, Wood said: “Wherever he got it, it did not come from us.”

Mustian’s story, accompanied by Gerald Herbert’s photos of the scene of the sting, was among the most-clicked and most-engaged stories of the week, with more than 300,000 pageviews on AP News and prominent placement on such websites as ABC News, PBS and The Washington Post. It also generated multiple tips to AP of similar abuses.

For deep reporting that exposed a horrific case and took a hard look at a common but loosely regulated type of police operation, Mustian earns AP’s Best of the Week — First Winner honors.