Does no one think that with that much money in his wallet, he wouldn't have simply memorized the private key in addition to storing it somewhere? The keys aren't really that long or hard to memorize and I would certainly remember mine if I had any significant amount of money tied to it.
Yeah, you would think that, but you'd also think he wouldn't have made a number of other pretty elementary mistakes that led to him getting caught, like promoting the website using a username linked to his email address (firstname.lastname@gmail.com), asking for help programming TOR services using his real name then quickly trying to delete his name, twice paying to have people assassinated that resulted in him getting conned (once to the FBI), and ordering fake IDs online to be sent to his residence under his name.
Yes. According to the paper they not only transferred the money, and they did it in 445 chunks of 324 bitcoins each (and one chunk with the remainder).
So in theory it's "seized" ... if they can brute force / guess the password.
But in practice, with access to a computer, DPR could probably transfer the contents from the address to a new wallet.