A former federal agent has shown in a courtroom that he traced hundreds of thousands of bitcoins from the Silk Road anonymous marketplace for drugs directly to the personal computer of Ross Ulbricht, the 30-year-old accused of running that contraband bazaar.

 In Ulbricht's trial Thursday, former FBI special agent Ilhwan Yum described how he traced 3,760 bitcoin transactions over 12 months ending in late August 2013 from servers seized in the Silk Road investigation to Ross Ulbricht's Samsung 700z laptop, which the FBI seized at the time of his arrest in October of that year. In all, he followed more than 700,000 bitcoins along the public ledger of bitcoin transactions, known as the blockchain, from the marketplace to what seemed to be Ulbricht's personal wallets. Based on exchange rates at the time of each transaction, Yum calculated that the transferred coins were worth a total of $13.4 million.