A disturbing police-involved shooting occurred in St. Louis on Tuesday, amid weeks-long protests over the killing of an unarmed teen in Ferguson, Missouri.

St. Louis police shot and killed 25-year-old Kajieme Powell, who approached them with a knife. A store owner called the police after Powell refused to pay for some energy drinks and pastries and started pacing and yelling erratically in front of the store.

The police released the video below, filmed on a witness' cellphone, showing the entirety of the incident.

WARNING: The footage contains graphic and disturbing moments.

The relevant footage starts around 1:20, when the police pull up to street.

Powell starts to approach the two officers and pulls an object out of his pocket. As he moves closer, officers repeat "drop the knife" multiple times.

"Shoot me now, motherf*****," Powell responds.

Around 1:40, with Powell about a sidewalk's distance away, both officers open fire, shooting at least 10 times and killing him.

After reading many of the legitimate concerns surrounding the incident, Business Insider spoke with Chuck Drago, former police chief and now a law enforcement consultant. He broke down the officers' actions that day, concluding they acted "reasonably and legally."

"The officers didn't really have any choice but to defend themselves except with deadly force at the point," Drago said, after viewing the footage for the first time.

If an armed individual moves within 10 feet of an armed officer, that officer has the right to use deadly force, according to Drago. "That's when an officer knows he's in danger," Drago explained. Police also need to consider bystanders' safety.

"What the officers should have done, or I hope they would have done, is control him or contained him, but I think there was enough urgency here," Drago said.

Still, many people may wonder why the officers didn't tase Powell first.

"A taser may not be effective, and then if it's not, he's on top of the officers," Drago said. "Other tactical options are risky. And if they don't work, the officer could be stabbed to death. At this point, the officer needs to make an urgent judgement call."

The information, if any, officers have ahead of an encounter with a suspect, however, should influence their response to a situation.

For example, if police officers know a suspect might be experiencing a psychotic episode, they will sometimes send a specially trained officer. Whether St. Louis employs these officers remains unclear, but the police report shows multiple people called 911 and described Powell as armed and erratic — potentially hinting at a mental disorder.

In general, police should not behave aggressively or move too quickly and try to establish a rapport with a mentally disturbed person, Drago explained. Powell failed to respond to the police's commands, though.

"The officers didn't have time to develop a rapport in this situation. They were put on the defensive as soon as they arrived," he said.

St. Louis police chief Sam Dotson speaks to the media after Powell's shooting. Screenshot via QFox13

As the police chief continues looking into this matter, Drago said, he should consider whether the officers could have or should planned ahead in order to handle the situation better.

Thus far, police chief Sam Dotson has promised absolute transparency.

"I think this chief has done a much better job of dealing with this than other places," Drago explained. "He's making an effort to get the information out as quickly as possible."

In interviews, Dotson has said Powell raised his weapon when approaching the officers. Neither the police report nor the footage show that, as The Atlantic noted. Dotson could have simply made a mistake when he said Powell raised his weapon, but Drago acknowledges the chief should correct the misinformation.

And what about shooting to disarm him?

Contrary to what you see in film, police aren't trained to shoot to disarm. "Officers are trained to shoot for center mass," Drago said. "They don't try to shoot the gun or knife out of his hand because ... he's probably not going to hit it, and those few seconds are lost."

The officers also fired at least 10 shots, but police commonly shoot suspects multiple times.

The St. Louis officers responsible for shooting and killing Powell may have followed the proper procedures — but whether these protocols require re-evaluation is another discussion.

"I'm a firm believer that you deal with the mentally ill in a different way," Drago said. "Some departments are more progressive than others when it comes to this."