PARKLAND, Fla. -- President Trump on Monday criticized former school resource deputy Scot Peterson for not entering the building to confront the gunman who killed 17 people in Parkland, Florida. Now Peterson is fighting back.

In a statement, his attorney said the first call Peterson received was for "firecrackers" and "not gunfire." When he actually heard shots, Peterson's lawyer said he believed they were coming from outside the school.

"Consistent with his training, [Peterson] took up a 'tactical position' between two buildings," his lawyer said. A radio transmission about a possible victim by the football field, "served to confirm Mr. Peterson's belief that the shooter, or shooters, were outside."

Jeff Bell, president of the union for Broward County deputies, questions Peterson's claims, noting that more than 100 rounds were fired over six minutes.

"So with that information, you know, where those rounds are being fired from, you better get your butt inside that building," Bell said. "Because it doesn't matter if you actually kill the shooter, there are plenty of circumstances in past scenarios where shooters have simply given up because they saw a uniformed police officer making entry."

The sheriff's office said it was also investigating reports that three other deputies stayed outside and whether two of 16 calls about suspect Nikolas Cruz's behavior before the shooting were properly handled.

Florida Gov. Rick Scott has now called for a state investigation and more than 70 Republican state lawmakers signed a letter urging the governor to suspend Sheriff Scott Israel, who refuses to step down.

"I can only take responsibility for what I knew about I've exercised my due diligence," Israel told CNN.

Student activists and their supporters are keeping the focus on pushing for stricter gun laws. Survivors returned to campus Sunday ahead of the start of classes.

"I want to walk into school with my head held high because I know that's what they would've wanted," one student said.

Classes are scheduled to resume Wednesday with a half school day and grief counselors on hand. Teachers have already been allowed to return to the campus to prepare.

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