A couple years ago I was checking in for a flight (IND-PHL on US Airways) when at the other end of the counter I saw some sort of official flash a badge to the counter agent and have a discussion while an orange jump-suited man stood around behind him. After I got to my gate, I sat and watched as a flight to PHX boarded, pulled away, then returned to the gate and let all the passengers off for a few minutes. My memory is hazy as to what was stated by the gate agent, but I believe a mechanical problem was implied. After a brief wait, the passengers reboarded and the flight was off and away. It was the last flight to PHX for the day, and I figured the plane returned and passengers removed so that the prisoner could be boarded via the van method mentioned before, but I have no way to know for sure. I figured that would be the preferred method over bringing the plane back to the gate and walking the prisoner to the back past all of the other passengers.