that is not how they caught him. They used a correlation attack. He was stupid and posted something using his personal email on stackoverflow about setting up tor website and processing bitcoin transactions. He then used a linked account to advertise silk road a few times. This made him a prime suspect. They followed him for weeks and watched that every time dread pirate roberts logged in and posted on silk road he was sitting in a cafe or library on his computer connected to a vpn. This was enough for them to get a search warrant and they found all the other evidence they needed to convict him on his laptop

Do you have a source for that? I've never heard it before.

Nevermind, they chatted with him, but that was to ensure that he was logged in to SR before grabbing his laptop in an unencrypted state, not to identify him: https://www.wired.co/2015/01/silk-road-trial-undercover-dhs-...