A few years ago, Sen. Charles Schumer (D-N.Y.) urged the Drug Enforcement Administration (DEA) and Department of Justice (DOJ) to go after the operators of illicit online marketplace Silk Road – but feds must make sure to keep an eye out for “copy cat websites” which have continued to facilitate illegal drug sales, he says.

Earlier this week, Sen. Schumer said in a statement that federal law enforcement officials should do a “top to bottom investigation of how these online drug marketplaces continue to thrive, and whether we must better prioritize combating these sales.”

Last October, the FBI shuttered Silk Road, but a number of other sites have cropped up since then, Schumer said, “which can be more difficult to target than one centralized marketplace.”

Schumer cited a Newsday story, which highlighted that the number of “encrypted dark web” sites selling illegal drugs doubled since last year.