A former US Secret Service special agent pleaded guilty to taking more than $800,000 of electronic Bitcoin currency while investigating the "Silk Road" online black market, the Justice Department said.
The "Silk Road" was a website where sometimes illegal transactions could be conducted secretly in Bitcoin. The site's creator was sentenced to life in prison in May for charges including money laundering and drug and drug trafficking.
Former Secret Service member Shaun Bridges, 32, pleaded guilty to money laundering and obstruction of justice over taking the Bitcoins while assigned to an electronic financial crime unit during the investigation.
The Secret Service is charged with the protection of the US president and other national leaders and also investigates counterfeit currency and other financial crimes.
Bitcoin is a virtual currency that has no central bank or government backing it, and is instead regulated by users.
Bridges is scheduled to be sentenced by a California judge in December.
"Mr. Bridges has now admitted that he brazenly stole $820,000 worth of digital currency while working as a US Secret Service special agent, a move that completely violated the public's trust," US Attorney Melinda Haag said in a statement about the case.
According to his statement, Bridges used an administrator account to enter the Silk Road website and transfer Bitcoins to the account he controlled.
The money was transferred to another account in Japan before being returned to the US and sold for a sum of $820,000, the government said.
Another former agent, Carl Force, also recently pleaded guilty to charges involving a theft of more than $700,000 in digital currency, the US said.
Earlier in August, the head of another Bitcoin exchange known as MtGox was taken into custody in Japan over allegations he manipulated data to create $1 million worth of the digital money.