Sometimes, you don't even have to hit the right target...
In a previous job, I was asked to investigate a problem with internet speed (Megastream 2 for a campus site - 'nuff said), and I discovered that someone had been viewing lots and lots of porn vids at the time the problem occurred.
So, I passed the information on to the offender's department. To my surprise, TWO people 'fessed up - it seems that two machines had been swapped behind my back, and my records weren't up to date.
#1 offending IP now belonged to another staff PC, and "words were had" - but the person I had accused turned out to be #3 on the bandwidth report, and he realised that the jig was up.
I didn't believe on bringing disciplinary action down upon people for stuff like that - departmental secretaries giving academics the "I know what YOU did in the comfort of your office last night" Laser Stare of Doom was far more effective, and meant less paperwork for me.
Biting the hand that feeds IT
