SAN FRANCISCO (CBS SF) — Five years after Ross Ulbricht, founder of dark web marketplace Silk Road, received to a double life sentence in prison, federal prosecutors filed a civil complaint Thursday seeking the forfeiture of thousands of Bitcoins seized by law enforcement on Tuesday that were valued over $1 billion.

A New York federal jury found Ulbricht guilty in 2015 of seven criminal counts, including conspiracy to distribute narcotics and money laundering. Yet since Ulbricht’s arrest years before as he sat in a San Francisco public library, federal agents have been trying to unravel the financial web spun by the illegal dark web marketplace.

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“Silk Road was the most notorious online criminal marketplace of its day,” said U.S. Attorney David Anderson in a news release out of his San Francisco office. “The successful prosecution of Silk Road’s founder in 2015 left open a billion-dollar question. Where did the money go? Today’s forfeiture complaint answers this open question at least in part. $1 billion of these criminal proceeds are now in the United States’ possession.”

According to the allegations of the civil forfeiture complaint, from 2011 until October 2013 when it was seized by law enforcement, Silk Road was the most sophisticated and extensive criminal marketplace on the Internet.

Prosecutors said the virtual online marketplace served a sprawling black market where unlawful goods and services were bought and sold regularly by the site’s users.

The complaint further alleged that while in operation, Silk Road was used by thousands of drug dealers and other unlawful vendors to distribute hundreds of kilograms of illegal drugs as well as other unlawful goods and services to well over 100,000 buyers, and to launder hundreds of millions of dollars derived from these unlawful transactions.

At the time it was taken down in 2013, Silk Road had nearly 13,000 listings for controlled substances and many more listings offering illegal services, such as computer hacking and murder for hire. Silk Road generated sales revenue totaling over 9.5 million Bitcoins and commissions from these sales equalling over 600,000 Bitcoins.

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The complaint further alleges that Silk Road used a so-called “tumbler” to process Bitcoin transactions in a manner designed to frustrate the tracking of individual transactions through the cryptocurrency Blockchain.

“Criminal proceeds should not remain in the hands of the thieves,” said Internal Revenue Service Criminal Investigation Special Agent in Charge Kelly R. Jackson in a news release. “Through CI’s expertise in following the money, we were able to track down the illicit funds.”

The complaint further alleged that in 2020 agents of the IRS CI used a third party bitcoin attribution company to analyze bitcoin transactions executed by Silk Road. Agents identified 54 previously undetected bitcoin transactions executed by Silk Road, all of which appear to represent Bitcoin that was stolen from Silk Road around 2012 and 2013.

The funds were traced to a bitcoin address. Further investigation of that bitcoin address by the United States Attorney’s Office and IRS CI agents revealed that the funds were connected to Individual X.

It was further determined that Individual X had hacked the funds from Silk Road. Pursuant to that investigation of the hack, law enforcement seized several thousand Bitcoins on Tuesday.

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The civil complaint merely alleges that certain property is subject to forfeiture. The United States must prove, with of preponderance of the evidence, that the items are subject to forfeiture. If the United States prevails, the court will order all interests of any potential claimant forfeited.