Almost 80% of the Bitcoins received by Dread Pirate Roberts (DPR), the pseudonymous head of the Silk Road digital black market, may not have been seized by the FBI, according to new research by two Israeli computer scientists.

When the FBI seized the Bitcoin wealth of DPR, believed to be 29-year-old San Franciscan Ross Ulbricht, it published the address to which it moved the money. Now, Dorit Ron and Adi Shamir have examined the "blockchain", the public record of every Bitcoin transaction ever made, and identified not only the accounts from which the FBI transferred the 144,000 Bitcoins (presently worth $115m) it seized from DPR, but also several other accounts which appeared to be under his control.

Around a third of the Bitcoins which entered the accounts the FBI seized were moved back out of those accounts prior to the seizure. Some will have been spent, on running Silk Road and paying DPR's living expenses. But the researchers also believe that he had other accounts which the authorities have failed to access entirely.

For the months of May, June and September 2013, the DPR-run accounts received no income from the Silk Road itself. As the site operated on a commission model, taking around 7% of each sale, they conclude that the money for those months must be hidden elsewhere.

"Assuming that DPR continued to receive at least some commissions from Silk Road during these months," they write, "it seems likely that he was simply using a different computer during these periods, which the FBI had not found or was unable to penetrate."

Moreover, going by the known volume of Silk Road transactions – more than 9.5m Bitcoins were spent on the site – then around 633,000 Bitcoins will have been generated in commission. That would mean that the FBI's seizure represented just 23% of the site's gross income.

The research backs up reports from October that the FBI were unsuccessfully struggling to seize a further 600,000 Bitcoins belonging to DPR.

As well as highlighting the difficulty the authorities have in dealing with technologies like Bitcoin, the paper also underscores one of the most popular misconceptions of the currency: that it is anonymous.

While Bitcoin payment addresses need not have any direct link to the person or organisation using them, the decentralised nature of the currency requires transactions to be public. As a result, it is sometimes possible to look at the pattern of transactions carried out by one payment address and deduce who owns it.

The researchers also report on the possibility that Satoshi Nakamoto, the pseudonymous inventor of Bitcoin, may have been connected to DPR. Nakamoto, who invented Bitcoin in 2009 and provided the computer power which ran the network for the first year of its life, stopped communicating with colleagues in 2010, and hasn't been heard from since.

But the researchers find that one account, which sent a thousand Bitcoins to DPR in 2013, is linked through a string of high-value transactions to an account which has been active since 16 January 2009, and so Ron and Shamir argue that it is "reasonable to assume" that the account was owned by Nakamoto. They speculate that the transaction "could represent either large scale activity on Silk Road, or some form of investment or partnership".

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