I'm a retired Army Criminal Investigator. Loved every minute of it. Every case was a challenge, and no two were alike.
Also liked helping people who needed it. One case I recall most fondly was a GI who was ETSing, and who got paid about $3k in leave and final pay, which he proceeded to put in a knife box in an awol bag, which he left in his car with his buddy when he went to sign out of the unit. When he got back, his buddy was gone, and so was the money. Not a big mystery, but the buddy denied knowledge and wouldn't take a polygraph. We had no other evidence, so I assigned the case to one of my apprentices as an interrogation exercise. To make a long story short, the apprentice questioned the suspect, got nowhere, then called me in. I played "bad cop," yelling at my apprentice, saying we were going to write the suspect as a subject, see that he was court-martialled, etc., then stormed out of the room, slamming the door. In no more time than it took for me to walk down the hall to check my in-box, the subject came charging out of the room with my apprentice right behind. "Well," I thought, "Nothing ventured, nothing gained." As they walked by me, my apprentice said, "We're going to get the money!" Mind you, there was nothing further to be done on the case when I initially got it -- could have had the apprentice write it as a final, unknown subject case, with no problem. But it gave me a lot of satisfaction that I took that extra effort to solve it, and, incidentally, provide some good training for my apprentice. A couple of weeks later, the office got a letter from the victim asking about his money. I dictated a letter back to him, saying we had recovered his money, that we still needed it for evidence, and that it would be forwarded to him by registered mail as soon as we were through with it. When I signed that letter, I felt 10 feet tall. THAT'S what being a law enforcement officer is all about.