Juan Carlos Nazario was sitting on a lakeside bench waiting to play soccer when he heard the staccato popping of gunshots outside Louie's on the Lake, a popular waterfront grill and pub in Oklahoma City. He ran to his car to get his gun and moved toward the sounds.

Bryan Whittle was driving with his wife, heading off for a Memorial Day weekend getaway, when he saw a commotion outside Louie's. He thought someone might be drowning, so instead of turning his truck onto the highway, he barreled into the parking lot to offer help. As he jumped out, what he learned stunned him: There was an active shooter just yards away, and wounded victims were holed up in the restaurant's bathroom.

Whittle, too, grabbed his gun.

In a matter of seconds, the two armed citizens became self-appointed protectors, moving to take up positions around the shooter, drawing their weapons and shouting for him to drop his. Time stretched and warped. There was an exchange of gunfire. The gunman was hit several times and fell. As Nazario and Whittle converged over the man to restrain him, police arrived. Unsure who was who, officers handcuffed all of the men and put them on the ground as the shooter bled out into the grass and died.

"I was just doing what I was supposed to do," recalled Nazario, a former police officer who said he now works as a security guard, always has his gun in the car, and usually carries it with him.

"I just reacted," said Whittle, who has served nearly 20 years in the Oklahoma Air National Guard and works for the Federal Aviation Administration. "There's a guy with a gun. I've got a gun. Stop the threat."

Though they were loaded into police cars and taken downtown for questioning, they were soon hailed as heroes. They were also called champions of Second Amendment rights, gun-carrying examples of why Oklahoma's Republican governor should not have vetoed a bill two weeks earlier that would have eliminated the need for a permit and training to carry a gun in public.

In a nation grappling with frequent mass shootings, Second Amendment activists have urged that more people carry guns so that they are prepared, like Nazario and Whittle, to respond to an armed threat. The morning after the May 24 Oklahoma City shooting, the National Rifle Association tweeted that it was "just another example of how the best way to stop a bad guy with a gun is a good guy with a gun."

Local police also praised Nazario and Whittle, saying their swift response ended what a police spokesman called "a very dangerous situation."

But police also noted that armed citizens can complicate volatile situations. The first of 57 uniformed police officers arrived just a minute after the initial 911 calls and found a complex scene with multiple armed people and no clear sense of what had happened or who was responsible.

"We don't want people to be vigilantes," Bo Mathews, a spokesman for the Oklahoma City Police Department, said in a recent interview. "That's why we have police officers."

Both men did what they believed was right, but that meant they had killed a man they did not know. Whittle wondered whether he was going to jail. Nazario went over ways that the confrontation could have ended differently — perhaps with his own death. They both marveled that amid the chaos, the result was as intended: The attacker was stopped before he could hurt anyone else.

It was about 6:30 p.m. when the shooting began. A man stood outside the main entrance of the restaurant and fired bullets at the façade, hitting a woman and two adolescent girls as they walked toward the glass doors. People inside panicked, rushing two of the wounded to a bathroom.

Nazario, 35, said he heard five or six shots before he retrieved his .40-caliber Glock handgun from his car and headed for Louie's.

He entered on the restaurant's lakeside corner, diagonally opposite the shattered main entrance, assuming the tactical stance he learned in firearms training. He crossed the room, assuring customers who had taken cover that he was there to help and asking where the gunman was.

Whittle, 39, learned about the shooting from Ron Benton, a Louie's patron who had slipped out to the parking lot after the shooting began. Benton pointed out the gunman, who was standing on a grassy slope, still holding a Ruger pistol.

Whittle grabbed his .40-caliber Smith & Wesson handgun from his truck, ran toward the gunman, and took cover among parked vehicles to the west.

Nazario, emerging from the restaurant's shattered entrance, also spotted the 6-foot-5 Benton pointing out the gunman and approached from the south.

Both men shouted at the gunman, with Whittle yelling: "Drop your weapon! I will shoot. Just drop it!"

When the man did not respond, Whittle noticed he was wearing protective earmuffs. Whittle took his left hand off his gun and began signaling his command. The man tilted his head, looked sideways, and raised his weapon. Whittle was staring directly down the barrel."It looked like a cannon," he said. Whittle dove behind an SUV as the man fired.

Nazario then fired, and he believes he hit the gunman in the thigh. He saw the man stumble forward, then right himself and raise his gun again. Whittle, now crouched beside the SUV, took aim and fired. Nazario fired four rounds and Whittle seven. The gunman collapsed.

As Whittle lurched forward to kick away the shooter's gun and check for other weapons, he heard a shout: "I got you covered. Clear him!" It was the first Whittle and Nazario knew of each other, and both made the snap decision that they were friends, not foes.

Whittle dropped his gun. Nazario holstered his. Nazario grabbed the dying man's right arm while Whittle took his left, just as the first police officer arrived, yelling at them both to get down.

"He doesn't know how many active shooters there were," Nazario said. "He could have gotten out of his car and shot me."

As police gained control of the scene, Jabari Giles, father of one of the wounded girls, rushed to the scene. Seeing Whittle and Nazario handcuffed on the ground and a bloodied body that he took to be a victim next to them, he exploded.

"Which one of you did it?" Giles shouted. "You f---ing shot my kid, didn't you!"

Giles did not have a gun, but police turned theirs on him and briefly handcuffed him before helping him locate his child.

One officer broke the news of the gunman's death to Nazario.

"I was kind of shaken up," Nazario recalled. "I thought he had made it."

Confusion was still rampant inside the restaurant. A waitress didn't know which way to run amid the shattering glass, upturned tables, volleys of gunfire. "We were told there were three shooters," she said.

"In all reality, there were three shooters," said Benton, the Louie's customer.

The FBI examined 160 shootings between 2000 and 2013 and found that most of the violence ended when the assailant stopped shooting, committed suicide, or fled. Unarmed citizens successfully restrained shooters in 21 of those incidents, according to the FBI. Two attacks stopped when off-duty officers shot and killed the attackers. Five ended in much the way the attack at Louie's did — when armed civilians, mostly security guards, exchanged fire with the shooters.

In November, Stephen Willeford, a former NRA instructor, shot a gunman who killed more than two dozen people inside a church in Sutherland Springs, Texas, hitting the attacker twice. The shooter fled and later shot himself in the head while under chase. And in June, a pastor and volunteer firefighter who had been through active-shooter training killed a carjacker who opened fire inside a Walmart store in Tumwater, Washington.

But interventions by "Good Samaritans" also have ended in tragedy.

In 2014, husband-and-wife attackers killed two Las Vegas police officers before going into a nearby Walmart and firing a shot in the air. Joseph Wilcox, 31, a civilian with a handgun and a concealed-carry permit, pulled his weapon to confront the male shooter, but the man's wife shot Wilcox in the chest, killing him.

When Prince George's County police detective Jacai Colson responded to a 2016 attack on a police station in his street clothes, another officer mistook him for a threat and fatally shot him.

Ronal Serpas, former police chief in New Orleans and Nashville who lived near Tumwater when he was chief of the Washington State Patrol, said such situations raise life-or-death concerns for police.

"How is the officer going to discern who is the Good Samaritan and who is not?" Serpas said. "They don't have placards on the front of their shirts that say 'I'm the good guy' or 'I'm the bad guy.'"

Three patched bullet holes on an outside wall at Louie's show where the gunman — Alexander Tilghman, 28 — had fired on customers. The restaurant's glass entryway has been repaired. The three people who were shot as they walked in are expected to make full recoveries, though the two girls have undergone several surgeries.

Nazario and Whittle had no idea who Tilghman was when they killed him. Tilghman did not kill anyone, and any sentence he might have faced had he been apprehended certainly would have been less than death.

Though Tilghman did not have extensive interactions with police, his behavior had been raising concerns in Oklahoma City. Local news reports before the shooting indicated that Tilghman had posted fliers around the city alluding to "demons in cloned transsexual bodies," and a local television investigative reporter alerted authorities to Tilghman's "bizarre" online postings. Tilghman was licensed to carry a weapon and had been through training that would have included a psychological evaluation.

Prosecutors took three weeks to conclude that Whittle and Nazario would not face charges; authorities determined that the men had been protecting themselves or others when they opened fire on Tilghman.

Neither Nazario nor Whittle knows who fired the fatal round or rounds. The medical examiner listed the manner of the gunman's death as "homicide" as the result of "multiple gunshot wounds."

"It is what it is," Whittle said. "You'd better be damn sure that what you are doing is right, because you'll pay the consequences if you are wrong."

An Oklahoman who grew up among family members who taught him how to handle guns, Whittle vigorously defends the right to bear arms. He notes that not everyone takes action in perilous moments, even in a place where many people carry weapons. "Think about all the people that probably had a gun and didn't go to the situation," Whittle said. "I was comfortable enough to just react."

Nazario, who also grew up with guns, emphasizes the importance of the numerous firearms training courses he has taken. "Not everybody knows what they are doing," he said.

In the weeks since the shooting, he has replayed in his head different endings to the incident. What if instead of retreating to the grassy bank, the gunman had followed his initial shots through the broken glass door into the restaurant? And what if Whittle had followed the gunman inside?

"Bryan would have entered the front," Nazario said. "I would have entered the back." There they would have been, two good guys with guns, face to face.

"He could have thought I was the shooter," Nazario said. Or vice versa. And if Nazario had asked — and Whittle refused — to drop his weapon, Nazario said, "I would have had to take action."

Excerpted from an article that originally appeared in The Washington Post. Reprinted with permission.