Here's an interesting article on how the US govt seizes the assets of criminals:
http://fortune.com/2018/02/21/government-forfeiture-bitcoin-auction/Enterprising agents figured out ways to snag suspects’ currency when it wasn’t protected. To get Ulbricht’s Bitcoin, they snatched his open, unlocked laptop from under his nose while arresting him in a San Francisco library. (As for Cazes, he was logged in to an AlphaBay administrator’s account when agents rammed a car through the gate of his Thailand estate.) By the time they busted the Dread Pirate, the marshals had got up to speed: They controlled at least two digital wallets of their own, to hold the Silk Road currency and receive Bitcoins seized by other agencies. “This was cutting-edge stuff,” says Sharon Cohen Levin, a longtime chief of the asset-forfeiture unit in the U.S. Attorney’s office for the Southern District of New York, and now a partner at WilmerHale. “We’d never done something like this.”
