CHICAGO — In this city’s urgent push to rein in gun and gang violence, the Police Department is keeping a list. Derived from a computer algorithm that assigns scores based on arrests, shootings, affiliations with gang members and other variables, the list aims to predict who is most likely to be shot soon or to shoot someone. Shaquon Thomas was on it.

His first arrest came at age 13, and others quickly followed, his face maturing in a progression of mug shots. By 18, Mr. Thomas, who was known as the rapper Young Pappy, had been wounded in a shooting, the police said. Then, last May, Mr. Thomas, 19, was fatally shot in what the police said was a running gang feud. His score was more than 500, putting him near the top of the Chicago Police Department’s list.

“We know we have a lot of violence in Chicago, but we also know there’s a small segment that’s driving this stuff,” Eddie Johnson, the police superintendent, said in a recent interview.

The authorities hope that knowing who is most likely to be involved in violence can bring them a step closer to curtailing it. They are warning those highest on the list that they are under intense scrutiny, while offering social services to those who want a path away from the bloodshed.