One place I worked as looked after by a single BOFH, he got the bright idea that there was a better way to get rich than working for a living. For a whole month he made sure the backups didn't run, although he signed them off as successful.
Then one Saturday he came into work:-
Took a full backup to several tapes
Deleted all files on all disks (including the OS)
Took the tapes home in the back of his car.
He then made a call to his boss telling him what had happened and demanding a ransom for the backup tapes. The boss made 2 phone calls, one to the system vendor who sent a team onto site to 'undelete' all the data (If he'd been brighter he could have erased the data but as with many OS's simply deleting it left it on disk and you just had to find it to recreate the files) ; the second call was to the police. Then on the advice of the police he arranged the meet to hand over the ransom and this dimwit chose the car park of a Motorway services to do the deal, so it wasn't really difficult for the Police to cover all the exits!
The system was back up with minimal impact, although it cost a bit to pay the vendor for the consultancy.
He went down for extortion.