A judge for the US District Court for the Southern District of Florida on Tuesday sentenced Guy Vallerius, also known as “Oxymonster” on the dark web, to 20 years in prison for charges related to drug trafficking and money laundering.

The South Florida High Intensity Drug Trafficking Area Task Force led the investigation that uncovered Vallerius’ involvement in the illegal activities. Vallerius pleaded guilty in August to conspiracy to possess with the intent to distribute controlled substances and conspiracy to launder money, and forfeited 99.98947177 bitcoin and 121.94805811 bitcoin cash.

Vallerius is known on the dark web for selling Oxycontin and Ritalin under the alias “Oxymonster.” He worked for Dream Market, an online criminal website, as an administrator and senior moderator, supporting daily drug trafficking transactions between buyers and vendors, and laundered “illicit proceeds using virtual currencies.”

The US government has shown increased efforts in recent years to target criminals on the dark web. Last July, the US Department of Justice (DOJ) together with the FBI, seized and shut down AlphaBay, a criminal marketplace on the dark web. The site was used to sell numerous illicit products including illegal narcotics, computer hacking tools, malware, firearms, fraudulent identification documents, counterfeit products and toxic chemicals. In 2015 the DOJ indicted a Turkish man for allegedly organizing three cyber-attacks that led to an estimated $55 million in global losses. Also in 2015 a former US government employee with the Department of Energy and Nuclear Regulatory Commission was charged with a four count violation of federal law in connection with an attempted phishing scheme involving Department of Energy employee emails.