After my son boarded his first international UM flight, a young man was escorted in handcuffs by two police officers (I was still in the gate area). When I saw him board the plane and the officers exited, I went up to the desk to ask what was going on. In typical GA fashion, I was told that it was none of my business.
I was a little frantic (nervous mom) and threatened to do my best to shut down the airport and get my son off the airplane unless they explained the situation. A manager came to speak to me, and I was told it was an immigration issue, and it wasn't until the two police officers returned to the gate area to speak to me that I allowed them to close the jetway doors. I couldn't understand why a person who needed handcuffs and two armed officers escorting him through the airport was safe to fly unattended on a 6-hour flight. Once I was assured by the officers and the gate agents that this person was not sitting near my son, I calmed down.
I came home and started searching the internet for similar situations and explanations, and that's when I found Flyertalk.