June 13, 2019 11:30 a.m. update: US marshals shot and killed a man in Frayser, Tennessee, a north Memphis neighborhood, on Wednesday, sparking a protest that turned violent and left 24 officers, two journalists and an untold number of protestors injured.

The protest began when marshals were trying to apprehend Brandon Webber, 20, according to the Tennessee Bureau of Investigation, when Webber "reportedly rammed his vehicle into the officers' vehicles multiple times before exiting with a weapon," the bureau said. "The officers fired striking and killing the individual. No officers were injured."

Below is a story from 2016, following two fatal shootings by police officers, and describes police training that comes into play in a situation such as the one in Frayser on Wednesday.

Original story: 

People have taken to the streets in both Tulsa and Charlotte during the past week, protesting the fatal shootings of two men by police officers in those cities.

Those incidents, along with other high profile fatal shootings involving police in the past two years, have led some to ask the question – why do the police shoot to kill? Why not try to shoot to wound, instead?

While the question seems like a sound one considering the cases where unarmed people have been shot by officers, simply put, police officers shoot at people they perceive as posing a threat because that is what they are trained to do in order to end that threat.

Here's a look at why police don't shoot to wound instead.

Do officers really operate under a shoot-to-kill policy?

Police officers are trained to shoot as many rounds as necessary at the threat they are confronted with until the threat is neutralized – that is, they are trained to fire until the suspect is unable to shoot or in some other way injure the officer, other police or bystanders.

Why not “shoot to wound” instead?

For a couple of reasons: First, shooting to wound someone may not stop the threat. If a person is shot in the leg, the threat may still exist as a suspect could still use his or her hands to fire a gun or stab with a knife.

Second, and most importantly, it takes a skilled marksman to hit someone exactly in the arm or leg, and, most officers are not skilled marskmen. In fact, outside of an old-fashioned TV Western, few people can make that shot, no matter the training.

Dr. Bill Lewinski, executive director of the Force Science Institute, explained in a position paper for the Institute the physics involved in the notion of training officers – who are often running after suspects – to "shoot to wound."

"Hands and arms can be the fastest-moving body parts,” Lewinski said. “For example, an average suspect can move his hand and forearm across his body to a 90-degree angle in 12/100 of a second. He can move his hand from his hip to shoulder height in 18/100 of a second.

"The average officer pulling the trigger as fast as he can on a Glock, one of the fastest- cycling semi-autos, requires 1/4 second to discharge each round.

"There is no way an officer can react, track, shoot and reliably hit a threatening suspect's forearm or a weapon in a suspect's hand in the time spans involved.”

David Klinger, a professor of Criminology and Criminal Justice at the University of Missouri-St. Louis, put it another way speaking to ABC News -- with officers trying to stop a threat to their life or the lives of others, "Why would we want to injure or maim people?" he said. "It doesn't stop them."

What’s the law on police using deadly force?

Policy for the use of deadly force has been shaped by four U.S. Supreme Court rulings during the past 30 years.

A 1985 U.S. Supreme Court ruling struck down policies that allowed officers to shoot a suspect just because they are fleeing police. The court ruled that a suspect has to be posing an immediate threat of serious physical harm in order for police to justify using deadly force.

In 1989, the court went further saying officers can use deadly force if it is proven to be “reasonable” based on the circumstances of a specific situation.

The third ruling on deadly force came in 1994 when the court ruled that officers do not have to use less lethal force before resorting to deadly force – for instance, an officer does not have to use a Taser before he or she uses a gun in a situation.

In 2015, the court ruled citizens could not sue police for using deadly force against fleeing suspects unless it is "beyond debate" that a shooting was unjustified.

Candace McCoy, a professor at the John Jay College of Criminal Justice at the City University of New York, suggested in an article in The Guardian that shooting to wound would lower the legal threshold for using deadly force.

“As a policy, [shoot to wound] is a really bad idea because it would give the police permission to take that gun out of the holster under any circumstance,” she said.