SACRAMENTO (CBS13) — French authorities say they have little doubt the suspect who was stopped by three men from Sacramento was ready for a mass casualty attack.

Airman Spencer Stone, National Guard member Alek Skarlatos and Sacramento State Senior Anthony Sadler became instant celebrities after stepping in and taking down a man French authorities confirm is a terror suspect.

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A French prosecutor updated the world on the investigation into Ayoub El-Khazzani, 26, who was eventually hogtied by the Sacramento natives, along with others who helped. Despite claims by the suspect he was simply trying to rob people on the train, prosecutors say the Moroccan native viewed a radical Islamic video onboard minutes before the violence.

Security expert and active-shooter scenario trainer Hector Alvarez says the three men’s reaction was amazing, because many people simply freeze.

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“The most common reaction is that people literally just don’t do anything,” he said. “They cannot accept what’s going on. And you’ll hear things like, ‘Couldn’t believe it was happening,’ ‘It seemed like a skit.’”

Even in a post-9/11 world, he says what happened on that train is an example.

“It’s the mindset of somebody who is going to do what they have to do to get home, and do what they have to do to protect those around them,” he said.

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He says there’s no handbook for how to handle that kind of situation, and that’s it’s case-by-case.