Why do the police shoot to kill in the United States?

From Ferguson (Missouri) and North Charleston (South Carolina) to Tulsa (Oklahoma) and Charlotte (North Carolina): fatal police shootings seem to be occurring with alarming regularity.

Officials sometimes have to take the decision whether or not to fire their weapon in a matter of seconds and under pressure. It's not an easy job. However, some of the people the police have killed in recent years were unarmed, which has sparked strong anger in several communities across the United States and quite a few questions.

Why did the police have to kill these people? Is there another way to control a dangerous situation that does not involve shooting someone deadly?

These questions became stronger earlier this month after the suspect of being the attacker of New York and New Jersey, Ahmad Khan Rahami, was captured alive , though wounded during a shootout with police.

To understand the officers' perspective on their use of deadly force, CNN interviewed Cedric Alexander, a well-known national police expert and a veteran police chief. Alexander was called in to review the Ferguson Police Department (Missouri), after an officer fatally shot Michael Brown in 2014. He is also currently a Police Chief in DeKalb County, Atlanta.

This is a condensed version of our conversation.

Why do not the cops shoot to hurt?

The officers are trained in "shoot to stop," which usually results in homicide, Alexander explained. The target is fixed in the center of a person's chest because it is the target most likely to hit and, in addition, will shoot down the suspect.

Even for an experienced shooter it would be difficult to give the suspect a leg or arm when there is a fast moving situation. In addition, the injured person could shoot the policeman or someone else.

Why do officers shoot so many times?

Many of the policemen carry semiautomatic pistols instead of revolvers. Two decades ago, officers were trained to fire one or two rounds of their weapons and then assess whether they needed to continue firing.

However, now police are trained to calculate the level of risk while firing, which means the officer can pull the trigger several times before the suspect falls, Alexander explained.

Why do not they take a moment to reassess the threat while the police are firing?

An armed suspect is able to return the shots if the officer pauses, the expert said. Because semi-automatic weapons carry more bullets than six bullets and are easier to recharge, the doctrine of modern police insists on continuing to fire until the security forces and the public are safe.

Why not replace weapons with Tasers?

Legally, policemen are the only ones who can open fire when they feel that their life, or that of someone else, is in danger. However, some may perceive that threat differently. Although all officers are motivated to use non-lethal weapons to subject a suspect when they consider it viable, they may also use deadly force if they believe they are facing an imminent threat of injury.

That argument could easily be dismissed in the case of Tulsa, where the man who was shot had his hands in the air. In fact, the officer has been charged with murder. However, in Charlotte's shooting the position could be more debatable because apparently the suspect had a weapon that he refused to hand over, Alexander explained. The family discusses the fact that there was a weapon.

The Tasers have a range of about 10.67 meters, which allows the police to immobilize the suspects within the same distance from many armed confrontations. However, its safe and effective use requires "a lot of training" that many department does not provide, according to the National Police Training , a website training for security forces.

There are also reservations about the improper use that sometimes are given to the Tasers, leading to abuse by officials and, sometimes, with fatal consequences, explains the website.

(David Klinger, a renowned national expert on police issues at the University of Missouri, argues that officers should only use a taser if they believe they can prevent a situation from escalating to the use of deadly force. Considers that the Taser is an option when there is a second police that can offer "lethal cover", in case the electrical device does not stop the suspect).

With information from Brandon Griggs and Eliott McLaughlin