We still don't know what "delete" means in this context. Emails can be put in a trash folder but easily recoverable. They can be deleted but still exist on the hard drive and still recoverable with special software as long as the files are not overwritten. (see below) Or they can be deleted by wiping the file... a deliberate overwriting. I've no idea just what the FBI did... but if files were "wiped"... that is deliberately overwritten with special software designed to destroy them, then I don't believe that even the FBI could recover them.

If anyone is curious about what may remain on the hard drives even after deletion, there's a free data recovery program called Recuva put out by the same people that make CCleaner... a utility that cleans junk files from a PC.