Police say officers were on regular patrol when they drove up on an altercation in the 300-block of South Cicero Avenue around 11 p.m.
In what appears to be a plea for help, surveillance video shows a man flagging a passing police officer as he rolls through the intersection at Cicero and Gladys late on Memorial Day.
As a Chicago police squad car passes and stops a few feet away, the same camera angle shows two men begin a standoff, circling and stutter-stepping in the intersection before one swats at the other.
One man then trips and falls to the ground. A business owner's surveillance cameras captured the same attack from another angle, but ABC7 froze the videos right there, because police say what happened next was a violent attack.
In the part of the videos we're not playing, police say, by the time officers got out of their vehicle, one man repeatedly stabbed the other as he laid in the street.
At least 10 seconds passed before officers fired their weapons. In those precious seconds, CPD says, officers ordered the offender to drop his weapon, but he continued to attack the man on the ground.
Police say both the offender and the victim were hit by gunfire, and officers then rendered aid.
The suspect died at Mount Sinai Hospital. The Cook County Medical Examiner's Office identified him as 35-year-old Tracey D. Watson.
The victim was taken to Stroger Hospital in critical condition.
In the minutes after the shooting, the scene was swarmed by police and nearby residents.
The business owner said police have secured this security camera footage as well.
CPD says the use of deadly force is under investigation by the Civilian Office of Police Accountability, and the officers involved will now be on routine administrative duties for at least 30 days.
As for the victim, at last check, he remains at Stroger Hospital, listed in critical condition.