From the Time story William Anderson mentions below:
"I was on the phone with my brother. Somebody came down the aisle and put a shotgun to the back of my head and said put your hands on the seat in front of you. I got my cell phone karate chopped out of my hand. Then I realized it was an official."
In the ensuing events, many of the passengers began crying in fear, he recalls. "They were pointing the guns directly at us instead of pointing them to the ground," he says "One little girl was crying. There was a lady crying all the way to the hotel."
What would it have taken for this already harrowing scene to turn even bloodier? When you start pointing guns at panicky civilians and karate-chopping cellphones out of their hands, what are the odds that a passenger might break into hysterics or lose his temper? And what would the air marshals have done then?
