As an engine mechanic, Hanlons Razor comes to mind. We once had a "thief" in our garage who was stealing expensive welding gasses and getting away with it. So

As an engine mechanic, Hanlons Razor comes to mind. We once had a "thief" in our garage who was stealing expensive welding gasses and getting away with it. Sometimes she would steal whole tanks, other times she would siphon tanks until they were almost dry. We took to naming her Shirley. After about a month we caught the culprits. The tank theft was due to a manager in another location who was greedily stealing our gas bottles without filing the correct paperwork, to use at his location. The other thief was a gas safety relief system that measures tank temperature and pressure, and preemptively vents the contents if theres an irregularity. One of its 2 post sensors had died and the alarm for it was just being silenced by our cleaning crew.