Everyone knew Castiel belonged to him.
It's been that way since the day Castiel first arrived, shuffling quietly into Dean's cell, eyes downcast. Dean hadn't know what he was in for back then. He'd thought maybe something white collar. Castiel looked like the kind of guy who could have fiddled the books and he certainly had the brains for it.
Dean didn't know then that Castiel was a lifer like him. He didn't know that Castiel had killed one of his own brothers. Castiel had argued self-defense at his trial, but the jury hadn't seen it that way. Castiel had gone with a weapon and intent.
Dean didn't find that out until later, until he'd bribed one of the their guards to let him find out everything there was to know about 'Novak, Castiel.'
That first day all he knew was that Castiel was beautiful and he wanted him.
He made sure everyone else knew it too.
There was no one who'd risk crossing Dean.
It took Castiel a little while longer to figure out what Dean wanted from him, but as soon as he knew, he came willing, crawling into Dean's bed after lights out, offering all of himself up to Dean.
Dean wouldn't have had him any other way.