A US secret service agent who helped track down Silk Road mastermind Ross Ulbricht is to plead guilty to a string of fraud and money laundering charges.

Special agent Shaun Bridges worked as a computer forensics expert to help locate the website's servers, alongside undercover colleague Carl Mark Force, who communicated with Dread Pirate Roberts, the owner of Silk Road who was eventually revealed as Ulbricht.

But during the many months they spent posing as users of the site – and even a potential buyer of the entire business – Force and Bridges fell to temptation, with Bridges funneling $800,000 of bitcoins earned by Silk Road into his own bank accounts without authorisation.

A notice of Bridges's agreement with the prosecution was filed to a California court on 17 June, with a formal request that he will enter a guilty plea on either 31 August or 1 September, depending on court availability.

Part of the agreement will see the US government request Bridges returns any property traceable to his illegal actions, and he will be forced to pay "a money judgment equivalent to the amount of property" involved in his violations.

This amount is not known but in Force's case, he is accused of completing 10 wire transfers with money he earned from actions carried out on Silk Road. Nine of these were for amounts exceeding $99,000, with the largest being $225,000.

Silk Road was shut down by the FBI in October 2013 and Ulbricht was found guilty of creating, owning and running the website in February 2015. He was sentenced to life in prison with a chance of parole on 29 May.

The website ran on a part of the internet called the dark web, where sites are hidden from search engines such as Google and can only be accessed through a special browser called Tor; using Tor (and paying with the largely untraceable bitcoins) helped to hide the identity of Silk Road's vendors, customers and moderators.