Fort Lauderdale, Fla. • The armed school resource officer assigned to protect students at Marjory Stoneman Douglas High School took a defensive position outside the school and did not enter the building while the shooter was killing students and teachers inside with an AR-15 assault-style rifle, Broward County Sheriff Scott Israel said Thursday.

Israel said he suspended School Resource Deputy Scot Peterson on Thursday after seeing a video from the Parkland, Fla., school that showed Peterson outside the school building where the shooter was inside and attacking.

"What I saw was a deputy arrive at the west side of Building 12, take up a position, and never went in," Israel said.

He said Peterson was armed, and was in uniform, and should have gone into the building during the 6-minute event, which left 17 people, most of them teenagers, dead. When asked what the deputy should have done, Israel said: "Went in and addressed the killer. Killed the killer."

Peterson, 54, a resource officer at the school since 2009, resigned after Israel suspended him. Israel said two other officers have been placed on a restricted assignment pending an internal investigation relating the school shooting.

"They could have done more; they should have done more," Israel said. "It's a fluid investigation. They are on restrictive duty."

Attempts to reach Peterson on Thursday were unsuccessful.

Israel said that Peterson was in an office dealing with a school-related issue when the first shots were fired on Feb. 14 and that he got on his radio and then moved toward the outside of the building where the shooting was taking place. When asked what he is seen doing on the video, Israel replied: "Nothing."

"I think he took up a position where it looked like he could see the western-most entry into the building and stayed where he was," Israel said. "Never went in."

Israel said he "clearly" knew there was a shooter inside, something that made him "sick to my stomach."

"There are no words," Israel said. "These families lost their children. We lost coaches. I've been to the funerals. I've been to the homes where they're sitting shiva. I've been to the vigils. It's just, there are no words."

The revelation about the deputy comes as law enforcement officials and authorities have faced intense criticism for whether they missed previous chances to prevent the massacre. The FBI was warned last month about the shooter's potential for violence at a school, but failed to investigate that tip, while school officials, social services investigators and the sheriff's office had multiple encounters or troubling warnings about him over the years.

Israel's description of Peterson as an armed, trained officer who was present for a mass killing but did not confront the shooter also comes as President Donald Trump, in response to the Parkland massacre, has suggested arming teachers as a way to deter possible threats, while the National Rifle Association has also pushed for more armed guards in schools.

Trump has frequently suggested in response to mass shootings that more law-abiding people with firearms could help stop a shooter and the head of the NRA has repeatedly suggested the same. However, Israel's announcement Thursday suggested that even if a person is armed, trained and available to help, that may not stop a mass killing that unfolds in a matter of minutes.

The deputy's decision to remain outside breaks with police tactics for responding to active-shooting incidents. Ever since the 1999 attack at Colorado's Columbine High School, authorities have emphasized the importance of pursuing the attacker or attackers quickly in an effort to eliminate the threat and prevent additional deaths.

"Columbine resulted in new approaches in which patrol officers are being trained to respond to active shooters as quickly as possible," the Police Executive Research Forum, a think tank backed by major-cities chiefs, wrote in a 2014 report.

Of course, this approach brings with it inherent issues, the report continued, because "a faster response is more dangerous to responding officers. Patrol officers who quickly move to confront an active shooter face a high likelihood of being shot themselves."

Officers involved in responding to these shootings have later described the terror they felt. A report released by the Justice Department after the San Bernardino, Calif., terror attack quoted an officer who described checking room after room in the conference center where the shooting occurred, expecting to find the shooters behind the final doors.

"I don't want to say I made peace, but I was ready to go," the officer said. "We got into one room, and it was empty. We had a quick breath, and in we went to the last room. I was never so excited to not see anybody."

Reviews like that Justice Department study are regularly conducted after mass shootings, allowing officials to study how officers responded in order to determine what others can improve upon. Following the shooting rampages at the Washington Navy Yard, a movie theater in Aurora, Colo., and the Virginia Tech campus, authorities reviewed what they did and sought ways to improve future responses.

Peterson is mentioned as part of a 2016 social services agency investigation into Nikolas Cruz, the 19-year-old identified by police as the gunman. According to a Florida Department of Children and Families report detailing that investigation, Peterson was approached by investigators and "refused to share any information ... regarding [an] incident that took place with" the teenager.