ABC News' Ron Claiborne reports:
In every tragic mass shooting - Virginia Tech, Columbine and Aurora, Colo.'s deadly theater massacre on Friday - there are survivors - a fortunate few who managed to escape, hide or fool the shooters by playing dead.
Which raises the question: what can you do to survive if the unthinkable happens to you?
"Whether you are a 7-year-old child or a 70-year-old grandmother or grandfather, there are things that you can do to increase your chances of surviving," said Eric Greitens, a former navy seal and police trainer.
Whether you should you hide in place or make a run for it, Greitens said it depends on the situation - the farther you are from the shooter, the better your odds of escaping.
But if that is not a reasonable option, he said the next best move is to protect yourself by hiding or getting behind something - a wall, a desk, anything between you and the gunman.
"You might be hidden behind seats in a movie theater…the active shooter can't see you but those seats don't provide cover," said Greitens.
He said those seats those seats don't protect you from bullets as someone can shoot through those seats.
So if you cannot get away or hide, should you attack?
"Most people should try to evacuate but if you are faced with someone and they are two or three feet away and they've been killing other people, you want to viciously and aggressively attack because your life depends on it," said Greitens.
But experts disagree on whether playing dead is a good idea.
"I do not suggest playing dead but if you are really close to an active shooter you want to be an active survivor…if you are active survivor with people around you…your chances of survival are much higher," Greitens said.