Police in Philadelphia said at least 30 officers were injured Monday night during violent protests that erupted after a Black man armed with a knife was fatally shot by police earlier in the day.

USA Today reports more than 300 protesters marched on the streets of Philadelphia late Monday night into Tuesday. Dozens of officers were injured with rocks, bricks and other projectiles and a 56-year-old female officer was hit by a pickup truck and hospitalized with a broken leg.

A police cruiser was set on fire, and several businesses were looted.

At around 4 p.m. on Monday, officers responded to a report of a person with a weapon, according to police spokesperson Tanya Little.

Officers arrived at the Cobbs Creek neighborhood and encountered the man, 27-year-old Walter Wallace, who was holding a knife, she said.

Officers ordered Wallace to drop the knife, but he instead “advanced toward” them. Both officers then fired “several times,” Little said.

Graphic cellphone video purportedly shows the moments leading up to the shooting. It shows officers pointing their guns at Wallace as he walks in the street and around a car. He walks toward the officers as they back away from him in the street, guns still aimed at him.

Officers yell at Wallace to put down the knife. Two officers then fire several shots and Wallace collapses in the street.

Both officers were wearing body cameras, and have been immediately removed from duty.

John McNesby, president of the local police union, issued a statement saying “Our police officers are being vilified this evening for their job and keeping the community safe, after being confronted by a man with a knife. We support and defend these officers, as they too are traumatized by being involved in a fatal shooting.”

Philadelphia police commissioner Danielle Outlaw, the first Black woman to lead the city’s police department, acknowledged in a statement that the footage “raises many questions.”

According to the Philadelphia Inquirer, One witness, Maurice Holloway, said he was on the street talking to his aunt when he saw police arrive. Wallace had a knife and was standing on the porch of his home, Holloway said, and officers immediately drew their guns.

Wallace’s mother chased after him as he walked down the steps of his porch, still holding the knife, according to Holloway. His mother tried to shield Wallace and tell police he was her son.

Walter Wallace Sr., the man’s father, said his son appeared to have been shot 10 times.

“Why didn’t they use a Taser?” the senior Wallace asked outside a family residence on the block. “His mother was trying to defuse the situation.”

He said his son struggled with mental health issues and was on medication. “He has mental issues,” Wallace said. “Why you have to gun him down?”

We can’t presume to know what was in the officers’ minds as they drew their weapons and fired. That information will eventually come out during the investigation into the shooting.

Did they feel Wallace was close enough to justify lethal force?

Based on research conducted by Salt Lake City trainer Dennis Tueller in the 1980s, he found an attacker with a knife could cover 21 feet in about 1.5 seconds. His findings revolutionized law enforcement training.

This gave rise to the “21-Foot Rule,” the measure of distance that related to the time it would take an officer to recognize a threat, draw a sidearm, and fire two rounds center mass against an attacker charging with a knife or other stabbing weapon.

A defender with a gun, whether military, civilian, or law enforcement always has a dilemma. If he or she shoots too early, it could be murder. If too late, the risk is injury or death.

In 1.5 seconds, what would you choose?