MADISON, Wis. (CBS 58) -- An investigation is ongoing after a Madison Police Department officer shot and killed a man during an altercation. Video of the shooting that happened Wednesday, July 22, was shared widely on social media. 

On Thursday, community members gathered at the intersection where the shooting took place. A large memorial has formed for the man who was killed, Corey Ruiz. 

The shooting happened around 1 p.m. Wednesday. Police say they got a call that a man was stealing bicycles and checking vehicle doors. 

When police got there, they located Ruiz and he fled the area on a bike around 1:30 p.m. 

Police located him at the intersection of Baldwin and Williamson. 

Video shows the man take out a knife during the struggle. Police say Ruiz injured an officer as they attempted to arrest him. 

Officers deployed a taser, but police say it didn't work. 

The officer who was cut with the knife was also the officer who fired his weapon. 

The video circulating online shows the officer shoot Ruiz. People at the scene said they were shocked when they saw the video. 

“In disbelief the simple fact that they already had the knife out of his hands, his hands behind his back and it was already three or four police officers on him for your to pull out your gun and shoot him three or four times in the head and still give him CPR as if you think he is here and you know he is not is just diabolical to me," said Daborah Baker, protester. 

Four officers were involved in the incident. A second officer was injured during the arrest, and two others were not hurt. 

There is a vigil that will be taking place Thursday night at 5 p.m.