Larry Dean Harmon, 41, set up Grams in April 2014. Three months later he also set up on the dark web Helix, a so-called mixer or tumbler service that pools and swaps people's Bitcoins to obfuscate the original sources, according to court documents. You put your BTC into Helix and you get the equivalent amount of other people's out.

Larry Harmon, the man behind the Helix cryptocurrency mixer, has been sentenced to three years in prison after being convicted of laundering over 350,000 Bitcoin, valued at more than $300 million at the time.

Helix operator Larry Dean Harmon was sentenced Friday to three years in prison for laundering over $300 million in Bitcoin, primarily for darknet drug markets.