Experts on police response to mass shootings say it may be too early to condemn Broward sheriff’s deputy Scot Peterson for failing to act during the Parkland school massacre. But — from the information available now — it doesn’t look good for him.

“In training, we teach officers their first priority when they arrive is to stop the killing,” said J. Pete Blair, a professor of criminal justice and director of the Advanced Law Enforcement Rapid Response Training [ALERRT] Center at Texas State University in San Marcos.

“If there is an active shooter on scene, we train officers to ‘Isolate, distract, or neutralize’ the shooter as soon as possible,” Blair said.

Neutralize, in this context, means shoot to kill.

“Move to the sound of gunfire quickly and stop it,” is the default response that the training tries to instill in officers.

Peterson “had a handgun on him. He did not have a rifle,” Broward Sheriff Scott Israel told the South Florida Sun Sentinel on Friday.

Former Marjory Stoneman Douglas High School student, Nikolas Cruz, 19, used an AR-15 during the massacre, investigators said.

Asked if Peterson would have been afraid that he was outgunned if he encountered Cruz, the sheriff said: “Absolutely not.”

“Honestly to go into that situation, one would have a much better chance of winning with a rifle, but you go in with a handgun. You go toward the killer and you stop him from killing students,” Israel said

BSO deputies are issued automatic rifles, the sheriff said. Peterson apparently was not carrying his at the time.

Peterson, the school resource officer at the school since 2009, resigned and then retired on Thursday. He quit just hours after he was suspended without pay and placed under investigation.

Israel said Peterson should have gone in and “Addressed the killer. Killed the killer.”

Security video footage showed Peterson stood outside the school for four minutes or so while 17 students and staff members were gunned down, Israel said. Another 16 people were injured.

Law enforcement protocols changed after the April 1999 shootings at the Columbine high school in Colorado. At Columbine, the first officers who arrived on scene set up a perimeter to try to control the crime scene and waited for SWAT officers to show up.

Everything changed after that because many of the victims were killed or injured while SWAT officers were rushing to the scene. Trainers began teaching officers to immediately confront the shooter and try to reduce the body count.

Initial police response has also been criticized in other shooting massacres.

An officer confronted Orlando nightclub shooter Omar Mateen near the entrance to the Pulse night club in June 2016. But that officer figured he was outgunned, backed down and called for help. Mateen later barricaded himself inside the club, leading to a three-hour standoff before he was killed by police.

The Broward sheriff’s office standard operating procedure on active shooters states: “If real time intelligence exists the sole deputy or a team of deputies may enter the area and/or structure to preserve life. A supervisor’s approval or on-site observation is not required for this decision.”

That contact should continue until the shooter has either been forced to surrender, forced into a barricaded situation; been stopped; or the SWAT team takes over.

The center Blair leads has trained more than 113,000 law enforcement officers around the nation on how to respond to active shooters since 2002. Blair is also co-author of a U.S. Department of Justice analysis: A Study of Active Shooter Incidents in the United States Between 2000 and 2013.

Blair said that individual officers have to use their own best judgment in each situation and there is no blanket rule that an officer “should always do this or shouldn’t do that.”

But there are basic guidelines.

“If you arrive and your next officer is three seconds behind you, maybe you pause,” Blair said. But if the next officer is 10 minutes behind, he said the first officer probably shouldn’t wait.

Though Peterson has already given up his job, experts cautioned that investigators don’t yet have all the information they need to say what he should or shouldn’t have done.

“This officer has lost his career. It sounds like he won’t be able to stay in his community … He’s going to spend the rest of his life wondering what would have happened if he made a different decision,” Blair said.

Peterson deserves to have his perspective on what happened publicly released and considered, the expert said.

One local law enforcement expert, who did not want to be identified, said officers may choose not to go into a building if they have direct knowledge of an immediate threat, for example from a bomb squad, that a door is booby trapped or that some other catastrophic risk exists.

They may choose to stay back also if a gunman is firing an automatic weapon through a door, which would mean that police would not survive to render aid to anyone.

But unarmed coaches and teachers in the same situation ran toward gunfire to save high school students, Blair said: “That certainly makes it harder to say he shouldn’t have gone in.”

About half of active shootings end before police arrive on scene, according to research.

In cases where police arrive while the shooting is ongoing, close to one in four of those result in an officer being shot, Blair said: “We know these are very dangerous situations for the officers.”

Broward sheriff’s deputies have not participated in the ALERRT center’s training, according to the center’s records. But some staff from the sheriff’s office fire-rescue division have undergone some training there, Blair said.

The center, which has been endorsed by the FBI and uses current and former agents to handle training exercises, will examine three main aspects of the Parkland school massacre as the facts emerge.

Blair said his experts will scrutinize the initial police response, or lack thereof. They will also look at how first responders handled patients who needed medical assistance.

And they will study how law enforcement responded to tips about the Cruz’s conduct in the years, months and weeks leading up to mass shooting: “This guy [Cruz] appears to have put out many pre-attack indicators.”

Peterson was not a member of a union, said Jeff Bell, president of the International Union of Police Associations Local 6020, which represents about 1,350 road patrol deputies and sergeants in Broward County.

Bell said he spoke with Peterson on Thursday night to find out whether he was a member and needed services. He said Peterson was distraught and troubled by the attention he was attracting.

“I pray for his mental health, but I also pray for the mental health of all the first responders who did go into the building and saw things that some military veterans are never forced to see,” said Bell. He said there is no excuse for a law enforcement officer failing to confront an active shooter.

In last year’s fatal shooting at Fort Lauderdale Hollywood International Airport, Esteban Santiago surrendered when he saw armed deputies approaching him, Bell said. “How many lives could have been saved had Nikolas Cruz seen a uniformed deputy prepared to take him on? We’ll never know.”