You got a number of things wrong and we haven’t even got into the meat of it yet:

Tor said Ulbricht "made mistakes in operational security" and was caught by "actual detective work" rather than exploiting problems with Tor. Indeed, the FBI tracked him down in part thanks to an online post that linked to a Gmail account.

With Tor installed, the Silk Road URL directed new users to a black screen with a prompt for a username and password, as well as the option to sign up. All that was required to sign up for Silk Road was a username, password, and country of origin. "No other information is requested, and the country-location information entered by the user is not subject to any type of verification," Agent Tarbell wrote.

Though bitcoin transactions are tracked via a public ledger known as the Blockchain, it "only reflects the movement of funds between anonymous bitcoin addresses and therefore cannot by itself be used to determine the identities of the persons involved in the transactions," Tarbell wrote. "Only if one knows the identities associated with each bitcoin address involved in a set of transactions is it possible to meaningfully trace funds through the system."