In October 2013, the U.S. Federal Bureau of Investigation, apprehended Silk Road owner and operator Ross William Ulbricht, better known in the online black market bazaar as Dread Pirate Roberts. And as it is turning out, Ulbricht's arrest was very much his fault.

According to a declaration for Ulbricht's case (Unite States of America v. Ross Ulbricht), former FBI agent Christopher Torbell is claiming that the agency was able to track down servers for Silk Road by taking advantage of an IP leak due to a Captcha prompt on its login page.

Silk Road was on the Tor network to hide its IP address and keep its server location secret but a mistake on the part of Ulbricht led to the discovery of his site's server in Iceland. His lawyers, however, are arguing that the means used were illegal. This is why the prosecution's side had Torbell, who was part of the team that took Ulbricht down then, explain exactly how the Silk Road server was found in a declaration filed Friday.

"This did not involve accessing any administrative area or "back door" of the site. We simply were interacting with the website's user login interface, which was fully accessible to the public, by typing in miscellaneous entries into the username, password, and CAPTCHA fields contained in the interface," said Torbell in the declaration.

Torbell and another FBI agent analyzed individual data packets being sent back from the Silk Road website and noticed that some packets contained a certain IP address that was not associated with a known Tor node. Had the hidden service Silk Road was using been properly configured, it should've been sending out an IP address provided by Tor and not the actual IP address the site was using.

Torbell then used publicly available information to look further into the non-Tor IP address they discovered and found out it was assigned to an overseas data center in Iceland. Working with authorities in the country, subscriber information was obtained which led to a webhosting provider with a server showing high traffic volume from Tor. Further investigation alongside the Reykjavik Metropolitan Police turned up Ulbricht as the primary suspect.

If the judge accepts Torbell's declaration, this will throw a wrench in the defense's plan to use the angle that illegal means were used to acquire evidence, touching on Ulbricht's Fourth Amendment rights.

At the time Silk Road was shut down, about $3.6 million in bitcoins were seized by authorities.