I had a rather bizarre situation similar to this happen to me in MIA one day. We had been parking at one of the FBOs at MIA, until one day someone, we really never found out who, decided that we were too close to the street for security reason. This was suddenly discovered after seven or eights years of parking on this FBO ramp with no problems what so ever.
Never the less, Washington decided they knew more about this than we did, so we moved parking locations. New parking spot was now on a remote ramp just west of the main terminal complex and ramp, between the runways, next to the CFR station.
As luck would have it, I was the first AC/PIC/captain (take your pick) on a 727 to go to MIA and use this spot. The ramp was just big enough for a 727-200 to pull in and then do a 180 to face east as so to exit the ramp the same way we had come in.
So I taxi in, do the 180 and park. After parking I leave the aircraft and walk over to a group of police officers and police dogs that are standing next to a long white single story building. At first I thought that these K-9 units were something new for our ground security. Turned out that no they were not, but were there training the dogs for sniffing out explosives. As I am talking to them our regular ground support units show up with the prisoner transportation vehicles.
As the prisoner transfer starts one of the police officers I'm talking to gets a radio call. He answers and just a couple of seconds later he yells at the other K-9 officers that there is a bomb threat on one of the aircraft on the airport. Then I hear the fire trucks starting up at the CFR station on the other side of the ramp. Then the FE comes walking up to me in a hurry and tells me the same thing.
So all of us, the K-9 guys, the FE and I start looking around trying to see where the fire trucks are going and the police officer is on his radio trying to find out just where this aircraft is with the bomb onboard.
Turns out it is us.
Now we didn't have the same ground security as say Air Force One, but it's pretty tight when we are parked somewhere. Also this was our first stop that day from our home base. So the odds of someone planting a bomb on the aircraft is pretty low, next to really, really improbable. But, I wasn't paid for being an odds maker, I was paid to be a pilot, who was in charge of an aircraft loaded with over 100 prisoners in handcuffs and leg chains.
However, before I ordered an aircraft evacuation, I decided to find out just how viable this bomb threat was, where did it come from, who was called, etc. As we were checking this an airport truck drives up to us, you know the type, small white pickup, yellow flashing light on top drives all around airports doing God knows what. The driver gets out of the truck and walks up to us, then says, "I don't know why it took so long for anyone to take any action after I saw this aircraft sitting here on the ramp, but after I called in that there was an airplane with a bomb on board parked on the isolation ramp, I see things did finally start happening." (Or something like that.)
Apparently where we were parked, was the normal parking spot for aircraft with some kind of security threat. This guy saw us parked there, not surrounded by fire and police vehicles and had called in 'asking why there was no one responding to the aircraft with the bomb on it'.
I'll not repeat what I and the police officer told the guy in the airport truck. Needless to say I do believe that in the future he will ask for information before yelling 'Bomb' over the radio.
So while I did not order the aircraft to be evacuated, I was about 30 seconds from doing so. And if you think 100 plus regular passengers would cause problems running around after an evacuation, think what mayhem a 100 plus prisoners would have caused.