When I hire even the most junior staff, they have to go through a security clearance. I don't understand how the security clearance could miss this.
Was there something missing in the database, in terms of the hiring process? I know you mentioned this before, but I still find it hard to believe that it didn't pick up that he was a contractor. When you sign contracts, your name is on there and you have to submit it. As a prospective employee or one on probation, your name is on the DND contract.