AlphaBay, an online criminal marketplace operating on the dark web, has been seized, the Department of Justice announced Thursday. The move, according to U.S. Attorney General Jeff Sessions, was aimed at stopping the site's online of illegal drugs, including Fentanyl and heroin linked to overdose deaths.

"This is likely one of the most important criminal investigations of the year - taking down the largest dark net marketplace in history," Attorney General Jeff Sessions said. "I believe that because of this operation, the American people are safer - safer from the threat of identity fraud and malware, and safer from deadly drugs."

AlphaBay had mysteriously gone offline earlier this month after operating for the last two years. In addition to illegal drugs, the online marketplace also offered stolen and fraudulent identification documents and access devices, counterfeit goods, malware and other computer hacking tools, firearms and toxic chemicals. The operations to seize AlphaBay's infrastructure was led by the U.S. with cooperation from six other countries and the European law enforcement agency Europol.

Alexandre Cazes, known online as Alpha02 and Admin, a Canadian citizen living in Thailand, was arrested July 5 on charges of creating the site. He apparently killed himself on July 12 while in custody in Thailand, the Justice Department said. Authorities had filed suit against Cazes and his wife to recover assets alleged to have been obtained via the site, including millions of dollars in cryptocurrency.

At the time of the takedown, AlphaBay had more than 250,000 listings for illegal drugs and toxic chemicals and another 100,000 for stolen identification documents and counterfeit goods, making it much larger than the Silk Road dark web marketplace that was seized by law enforcement in November 2013.

The site operated on "Tor" network and used cryptocurrencies such as Bitcoin, Monero and Ethereum to hide the location of its servers, administrators and users. Based on law enforcement's investigation of AlphaBay, authorities believe the site was also used to launder hundreds of millions of dollars deriving from illegal transactions on the website.