The DOJ has announced that after a year-long undercover operation, they have arrested a number of dark web vendors selling illegal goods, including drugs and firearms. More noteworthy is the technique used by the investigators.

Motherboard reports that investigators from Immigration and Customs Enforcement’s Homeland Security Investigations (HSI) went undercover, posing as Bitcoin money launderers who could convert cryptocurrency into cash.

Nicholas Weaver, a senior researcher at the International Computer Science Institute at UC Berkeley, told Motherboard: “Posing as a money launderer for Bitcoin seems like a great mechanism to find the dealers: There are so many paths for the dark net dealers to get drugs. There are much fewer paths for them to get cash.”

While selling drugs on the dark web is not difficult, transferring the cryptocurrency made from those sales into fiat currency is. By posing as cryptocurrency launderers, feds were able to locate the original source of the drugs being trafficked. “Once you have the seller it is now easy to either find the drug dealer he’s supporting (by just following where HIS cash payments have to go) or, as they did here, take over the seller’s identity,” Weaver elaborated in the chat with Motherboard.

The Verge reports that the Bitcoin laundering service was an already existing business that was seized by feds in order to execute the sting operation. They also reported that in the past, feds were more concerned with taking down entire networks such as the Silk Road. Now, however, law enforcement officials have narrowed their focus to individual dealers. “When we take down a dark net marketplace, these criminals will move to other marketplaces,” HSI Special Agent in Charge Angel Melendez explained.

Motherboard noted that methods used to apprehend illegal dark web vendors in the past have included tracking the mailed packages of a drug dealer, deploying their own malware, and attacking the Tor network that many users use to connect to the dark web.

Get the full story at Motherboard.