I was on a NW flight about a year and a half ago when it was discovered maybe an hour before landing that a young woman had had all her "starting college money" and some other stuff (camera, etc.) stolen during the flight. Repeated PAs were made asking people to look carefully around their seat areas to see if they could find anything. Then the ante was upped and we were told that LEOs would be meeting the flight if the missing items weren't "found." Nothing. When the flight landed we were prohibited from unfastening our seatbelts until permission was given, even after the plane was at the gate. We sat & waited for a while, some TSA & local sheriff types were there when the door was opened & consulted for a while and then they finally announced that everyone other than people in some range of rows could finally unbelt and leave the plane. I got the heck out & never found out what happened, but always wondered. One of the FAs in first who looked like she had flown quite a few miles, shall we say, said she had never had such an experience. I don't think it is *that* common.