The dramatic takedown of the Silk Road drug market and the arrest of its alleged owner on drug trafficking and murder-for-hire charges last month began in part with an offhand tip to Department of Homeland Security investigators in Maryland in mid-2011.

The informant told DHS investigators in Baltimore about an online drug bazaar where international sales of illicit drugs and other contraband were conducted with impunity and with the ease of buying cocktail stirrers or underwear on Amazon.

“You guys are in law enforcement. You might want to look at this,” the informant told DHS investigators, according to federal law enforcement officials familiar with the case who asked not to be identified.

The informant directed investigators to the site, accessible only through the Tor anonymizing network, and explained how transactions for the sale of heroin, cocaine and LSD went down using the digital currency Bitcoin.