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