The Florida sheriff leading a state commission on the Parkland high school massacre says there were multiple opportunities to stop Nikolas Cruz during the attack – if only someone had confronted him with a gun.

Sheriff Bob Gualtieri of Pinellas County, citing surveillance footage taken from inside Marjory Stoneman Douglas High School, told a New York Times reporter Thursday that Cruz had to stop firing his AR-15 rifle several times in order to reload.

"If he had somebody in there with a gun, they could have mitigated this," the sheriff was quoted as saying. "There were opportunities for staff to have intervened if they had been armed."

Cruz, a 19-year-old former student at Stoneman Douglas, is charged with killing 17 people in the Valentine's Day attack.

Gualtieri added that during one of the reload breaks, a teacher was able to move his students to safety.

"There were several other times when he was in that school that his gun was empty," he also told the New York Times.

The comments came after prosecutors Wednesday released hours of video interrogation of Cruz, showing the young man slouching in a chair, being repeatedly urged by a detective to speak louder and punching himself in the face when he is alone.

Gualtieri told the Marjory Stoneman Douglas High School Public Safety Commission earlier this week that Cruz's fluctuating behavior through the years made it difficult for school officials to determine how he should be handled.

"It was really a roller-coaster with Cruz really from birth," Gualtieri said. A report released last week by the Broward County school district said he began showing behavioral issues that got him kicked out of pre-kindergarten. He spent his school years shuttling between regular campuses and those for children with emotional and behavioral problems.

"He had some really bad low times but at times he was without behavioral issues," Gualtieri said.

The video made public Wednesday shows Cruz hunched over at times, leaning back at others. He is seen wearing hospital clothes and speaking so softly at the beginning that Broward Sheriff's Detective John Curcio has to repeatedly urge him to talk louder. Shortly after entering a small interrogation room, the detective asks Cruz: "You all right? Got to be able to speak so I can hear you."

At one point, with the police out of the room, the video shows Cruz take two fingers, put them to his left temple and pretend to pull a trigger. He gave a little shake after doing this. Later, he is seen punching himself hard in the face with both hands and occasionally scratching at his right arm with a small object he picked up off the floor.

Much of the interrogation focused on a demonic voice Cruz claims he has heard inside his head for years that urges him to commit violent acts. When asked what the voice usually said, Cruz answered, "Burn. Kill. Destroy." He also said the voice told him to cut himself.

At another point with Curcio out of the room, Cruz mutters, "Kill me," and then, later, "I want to die."

The Associated Press contributed to this report.