Dr. Ben Carson is under attack for his comments about the Oregon college shooting, saying that he would have confronted the gunman and would have instructed people to attack the gunman.

Former Navy SEAL and FBI agent Jonathan Gilliam joined Megyn Kelly on "The Kelly File" tonight to explain how one should react in an active shooter situation.

Gilliam said that these incidents often only last between one and five minutes, so it's important to be prepared for the worst-case scenario.

He said there are four things that people should concentrate on beforehand, the first being understanding what critical areas and critical times to be aware of.

"If you go to that school at 3 a.m., there's nobody there. It's not a critical time," Gilliam said. "But it's very critical when school is in session. So you need to understand that."

He said the second thing is training the mind and forming an understanding of how to react and what to do in such a situation.

"You don't have to go out and learn how to box, but [train] in your mind," Gilliam said.

"Third thing is awareness. You need to be aware of what's normal, what's not, as far as behavior goes."

The last thing is deciding that you will take action now, not when the situation arises.

Gilliam said that action can vary based on the situation, but could include rushing the shooter, as Carson suggested, hiding or running.

Watch more above.

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