When Lt. Craig Cardinale got to Marjory Stoneman Douglas High School as a mass shooting was unfolding last year, he found Deputy Scot Peterson pacing outside, repeating, “Oh, my God. Oh, my God.”

The deputy, who was assigned to the school, was behaving in ways typically associated with fear or panic, the lieutenant told investigators. He was moving “back and forth,” talking to himself and “breathing heavily.”

What he was not doing was what the prevailing law enforcement protocol says was his first responsibility: Go into the building. Stop the gunman.

Peterson has been castigated and, as of this week, criminally charged with endangering children and culpable negligence in connection with the attack that left 17 people dead. The case against him is highly unusual and promises to raise all manner of legal questions, such as whether a police officer’s failure to perform as trained can lead to prison.

But it also raises a larger moral question: How much bravery do we expect, or demand, of law enforcement officers? What level of courage rises to the level of heroism — and what is just part of earning the paycheck?

Officers themselves are likely to hear inconsistent or even contradictory messages that may reflect the public’s polarized view of police as protectors or oppressors. Police officers rushed into the twin towers as they were collapsing; they have also shot and killed unarmed people for fear of losing their own lives.

“Every cop has heard some variation of ‘Your first job is to go home at the end of your shift,’ some version of ‘It’s better to be tried by 12 than carried by six.’ And every cop has also heard ‘You are the heroes; you are the front lines of defense; you are the ones who are supposed to run toward the gunshots,’ ” said Seth Stoughton, a former police officer who now teaches law at the University of South Carolina.

In many minds, the latter goes with the territory. “They have an obligation to put themselves in harm’s way,” said Ken Murray, who runs an association for training law enforcement and the military based in Orlando, Florida. “Now, if you don’t want to do that job, go do something else.”

But the idea of bravery and cowardice, in the world of policing, can be situational. What the public might think of as courage, one expert called “rational bravery” — behavior that is to be expected, given that officers with bulletproof vests and tactical expertise are the best positioned to respond and have been put in place to do so.

Expectations and training have changed drastically since the Columbine High School massacre in 1999, when law enforcement was criticized for failing to quickly confront the assailants and 13 people died. Until then, typical police protocol had been for officers to wait for backup, or for the SWAT team to arrive.

But after that, many departments rewrote policies to emphasize that every minute could mean another death. Officers were instructed to impede or take down the gunman immediately. Dan Oates, who was the chief of police in Aurora, Colorado, when 12 people died and 70 were wounded in a shooting in a movie theater there in 2012, said officers are now drilled in tactics that put the well-being of hostages and innocents first.

“That’s what you sign on for if this happens on your watch,” Oates said.

None of the officers who responded to the movie shooting hesitated to go in, said Lt. Jad Lanigan, one of the first to arrive, but that did not mean they did not feel fear; some had difficulty coping with the horror surrounding them and went into what he likened to a computer “blue screen.”

“I had people literally walk up to me, and they were blank-faced,” he recalled. “There was too much for the human brain to process. We had to take them out of it for a little bit, give them some clear direction, and they were able to plug themselves back in.”

“We expect more and more and more from our police,” said Murray, the law enforcement training executive. “They’re supposed to be expert marksmen, mixed martial artists, kind, caring nurturers, social scientists to the level of psychologists; they should be able to diagnose at a distance some poor individual who is downtrodden and acting out; we expect that they should be able to tell a real gun from an identical replica, and with very little training.

“If society knew how poorly officers are trained, they would never let them do this job.”

The criminal charges filed this week against Peterson in the Parkland case have injected a whole new potential calculation for officers to work through. Some policing experts said they feared that the threat of prosecution could have the unintended effect of pushing officers to act too quickly.

“Bravery should not be equated with running toward the danger no matter what,” said Maria Haberfeld, an expert on police training at the John Jay College of Criminal Justice in New York. “It really has to be understood and analyzed within the context of everything else that’s going on, and the officer’s discretion.”

If the idea of rushing toward gunfire plays to the hero in every officer, the narrative can change dramatically in cases involving claims of excessive force. In those cases, fear, not courage, is an officer’s best defense. Many officers have taken the stand to persuade a jury that they had reasonable cause to be afraid when they fired their weapon, even if in the end it turned out that they had misjudged the situation.

“I was scared to death,” testified Officer Jeronimo Yanez when he was on trial for the death of Philando Castile, a black motorist in Minnesota shot seconds after he told the officer that there was a handgun in the car. “I thought I was going to die.”

Be it heroism, or fear, or an officer’s safety, police often deploy whichever narrative seems to justify the use of force in such situations, Stoughton said, though they go into them knowing that some degree of risk comes with the job.

Officers are not often praised for pausing, instead of firing first, during those uncertain moments when a person being stopped reaches toward his waistband, or when a cellphone looks like a gun, and they are tempted to shoot first or face the possibility of being shot themselves. They rarely hear, Stoughton said, “Wow, you were really brave for accepting more risk than I would have.”

He recalled a traffic stop during his time as an officer in which he approached the passenger side of the car and caught sight of what looked to be a gun glinting in the driver’s lap. He raised his own weapon and asked the driver to put his hands on the wheel, then quickly ascertained that what he had seen was actually a Jesus medallion.

Every part of him was on high alert. He was afraid.

“If he had grabbed his medallion, ‘Jesus, help me here,’ I might have — not might have, I would have shot that guy,” he said.

The active shooter training that Peterson received made it clear how he was supposed to respond. It laid out what the Broward County sheriff’s office had identified as the “priorities of life” in descending order: “1) Hostages/victims, 2) innocent bystanders, 3) police/deputies and 4) suspects.”

But some experts say things are not always so clear and that officers have a duty toward even those they are policing.

“There is continuing tension about what officers should be taught about what to prioritize in situations where they’re confronting someone who seems disturbed and threatening,” said David Alan Sklansky, a former federal prosecutor who teaches criminal law at Stanford University.

“It is part of the job to put yourself in danger to protect other people. And I would say it’s also part of the job to put yourself in danger to protect the person that you’re trying to subdue.”

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