Roger Thomas Clark, an alleged operator behind the Silk Road darknet marketplace and adviser to founder Ross Ulbricht, pleaded guilty to “conspiring to distribute massive quantities of narcotics,” prosecutors announced Thursday.

The U.S. Attorney’s Office for the Southern District of New York said in a press release that Clark, who was known online as “Plural of Mongoose,” “Variety Jones,” “VJ” and “cimon,” pleaded guilty to one count of conspiracy and will be sentenced on May 29.

Clark was first charged with conspiracy to traffic narcotics and conspiracy to launder money in 2015. Prosecutors described him as a “senior advisor” to the platform at the time.

Silk Road is most famous for being a darknet marketplace where users could purchase illicit drugs and other goods using bitcoin as a payment method. Ulbricht is currently serving a life sentence in connection with his operation of the site, stemming from charges of narcotics distribution, computer hacking and conspiracy.

Ulbricht and Clark were both also accused of facilitating “the attempted killing of a co-conspirator,” though neither was charged in connection with this allegation.