I'm pretty sure the feds only have possession of the wallet. They can view the public key anytime and see what it contains. However without the password to decrypt the wallet, and most likely a password to "send" bitcoins (an assumption on my part, but it's pretty common practice to encrypt and password protect your bitcoin wallet) mere possession of the wallet doesn't mean squat. If he was smart and backed it up in the cloud somewhere all he would have to do is tell someone the account of where it's at and how to go about migrating into their wallet and give them the password to unlock the backed up wallet. The feds would hold a worthless piece of encrypted software at that point.
I have my wallet backed up to numerous locations outside of my own computer. Just because if one fails I'll always have a backup.