That would seem more plausible also because in that case the coins were not stolen, but simply lost. I would think that someone should have found the blockchain trail of the 750k BTC by now, if they were indeed stolen. It anyway took only few hours after the raid that people figured out the address[1] where FBI had deposited the coins seized from Silk Road.

[1] https://blockchain.info/address/1F1tAaz5x1HUXrCNLbtMDqcw6o5G...