In the aftermath, many have questioned why the deputy who fired his handgun did not try to disable Lopez by aiming for his legs or arms.

The most effective way to stop a threat is to shoot a suspect in the body, or "center mass," several experts said. A shot to the leg may not neutralize a suspect with a gun, they say, and shooting the gun out of a suspect's hand is the stuff of movies.

"Police officers are taught to shoot to stop a deadly threat," said Richard Lichten, a former law enforcement officer in Southern California and use-of-force expert. "No one wants to shoot someone, but faced with a deadly force situation, their options are limited. In a situation like that, you have three-fourths of a second to realize and act on the danger."

All law enforcement agencies train officers in the appropriate use of deadly force at least quarterly, said Raymond Foster, a retired Los Angeles police officer and former Petaluma resident. Officers are taught to fire in three-round bursts, he said.

Training involves simulations in which targets representing bad guys or innocent bystanders spin around and an officer has to decide whether to shoot, Foster said.

"The officer gets experience in making this quick decision in defending their life," he said.

Experts say that training has evolved in the past two decades as mass shootings involving increasingly younger gunmen have become more prevalent.

In the past, officers were trained to contain a gunman and wait until backup or a SWAT team arrived. Now, officers are taught to move toward the gunfire.

"Times have changed, and has forced police to employ more aggressive tactics," Foster said. "Twenty years ago, if you saw a 13-year-old with a gun, you'd think he's just out goofing off. But now we've had all these shootings done by very young children."

The day before the Lopez shooting, a Nevada 12-year-old shot and killed his teacher and wounded two classmates at school before killing himself.

The fact that Lopez carried a non-lethal airsoft rifle makes no difference to the officers who perceived the gun to be real, said Mike DeMarcus, owner of Law Enforcement Training Associates. The gun Lopez was holding lacked the orange tip that would have indicated it was non-lethal, according to Santa Rosa police officers investigating the shooting.

As a North Miami Beach cop, DeMarcus remembers chasing an armed suspect and ordering him to drop the weapon. The suspect, who complied with the order, turned out to be a 12-year-old boy with a pellet gun.

"If he would have swung it around, I would have shot him, no question," he said. "In a situation like that, you have a split second."

After a suspect is down, the threat is not necessarily over, experts say. Officers are trained to secure the weapon and detain the suspect before administering first aid.

On Tuesday, Lopez was handcuffed shortly after being shot. A medical team arrived three minutes after the shooting, authorities said, and was held at a distance for an additional two minutes before getting clearance to enter the scene.

The two deputies have been placed on paid administrative leave during the investigation, and they have received counseling, the Sheriff's Office said.

Law enforcement officials say that an officer-involved shooting can be traumatic for an officer.

"An officer replays the incident constantly in their head," DeMarcus said. "They will think 'Oh my god, did I do the right thing?' They know they will be judged for months to come. Whether they did the right thing or the wrong thing, they will have to live with it for the rest of their lives."