The chief executive of the Bitcoin exchange Mt. Gox has denied involvement in online black market Silk Road, following revelations from a Department of Homeland Security (DHS) agent that he had once been a prime suspect.

Speaking in the trial of Ross Ulbricht, who stands accused of making £11.9m off drug deals conducted via Silk Road, DHS agent Jared Deryegnan claimed that Mt. Gox chief executive Mark Karpeles had once been a suspect in their investigation into "Dread Pirate Roberts", the alias of the Silk Road chief.

"This is probably going to be disappointing for you, but I am not Dread Pirate Roberts," Karpeles said in an email to tech site Motherboard.

"The investigation reached that conclusion already – this is why I am not the one sitting during the Silk Road trial, and I can only feel defence attorney Joshua Dratel is trying everything he can to point the attention away from his client."

Emails read out at the trial in New York by Dratel showed that Deryegnan believed Karpeles could be using Silk Road to stabilise the value of Bitcoin, a cryptocurrency whose value has fluctuated hugely in the last year.

Drug dealers and hackers often make use of cryptocurrencies to monetise their activities online, owing the high level of privacy that the technology affords them. Silk Road also has to be accessed via the Tor network, providing another level of anonymity for criminals.

"I have nothing to do with Silk Road and do not condone what has been happening there," Karpeles continued in his email. "I believe Bitcoin (and its underlying technology) is not meant to help people evade the law, but to improve everyone’s way of life by offering never thought before possibilities."

The Mt. Gox exchange was forced to file for liquidation in Tokyo last year after a flaw in its code saw it lose 850,000 bitcoins, with the error blamed on hackers, and later received bankruptcy protection to secure its assets in the US.