The only problem with that theory is, if the employee wanted to do something illegal like selling the disk to someone else, then why report it at all? All he had to do was put it on a disk, sell it to his source, and keep quiet.
I think this could have been a "legitimate" burglary, being as he reported it to the police to alert officials of what was at stake.
You could be right but then it would be an unusual string of coincidences.