Yeah, if they didn't find a copy on the backup/original media to confirm it's zero bytes, then really all they've provided is their assumption that it's zero bytes.

I'm no lawyer, but the testimony of the IT guy (and associated reasoning/etc) seems like a totally different kind of evidence than a true and accurate copy of a file from an original medium. And having the IT guy testifying seems like way more of a pain than just making him find the file.