I agree, they do not have the right to make information like this vanish.However, they have a long practice of doing just that. The FBI confiscated tape from privately owned video surveillance cameras which recorded the Ryder truck pulling up in front of the Murrah Building with two occupants, and then recorded the explosion.
Those tapes have vanished.
I wish Grassely was as concerned about those videotapes as he seems to be about this package.