Tulsa's police chief has asked the Justice Department to join the investigation into the fatal shooting of an unarmed black man by a white police officer, after the release of video footage of the incident prompted outrage on Monday.

In the footage, which was recorded from a police helicopter camera and a dashcam in a police vehicle, Terence Crutcher, 40, is seen walking with his hands up, toward his SUV, which had stalled in the middle of the road. A police officer can be seen walking a few paces behind him, gun drawn.

In the helicopter video, an officer can be heard saying, "That looks like a bad dude too. He might be on something." Moments later, Officer Betty Shelby shoots Crutcher at close range. He falls to the pavement, where he remains sprawled out and motionless while officers decide how to react.

The incident occurred at around 7:30 p.m. on Friday, September 16. Dispatchers received a 911 call from a woman complaining about an abandoned SUV blocking the road. The caller added that a man was running from the vehicle, saying he was worried it would "blow up."

Crutcher's family has vehemently disputed the characterization of him as a "bad dude," describing him as a religious man who enjoyed singing at church every week.

"That big bad dude was my twin brother. That big bad dude was a father.... That big bad dude was enrolled at Tulsa Community College," his twin Tiffany Crutcher told reporters. "He just wanted to make us proud... the entire family is devastated."

Crutcher's family is seeking criminal charges against Officer Shelby.

At a news conference on Monday, Police Chief Chuck Jordan urged people to remain calm and promised that justice would be done. "I'm going to tell you right here now," Jordan said, "there was no gun on the suspect or in the suspect's vehicle."