Well, think of it from a liability standpoint. The department will get sued- and lose- if that weapon is ever used in a crime. As an officer, he should always be responsible for his weapon. What if he were to "forget" it and leave it laying about his house, his kid finds it and shoots himself/someone else? An officer should be more responsible than that. Actually, I was quite easy on him. Most departments would fire an officer on probation (almost all departments have a probation period, usually one to two years, when you are first hired) for a mistake like that. During probation, you can be fired for any or even no reason at all.
