Chicago police said 40 detectives, along with agents from the FBI and Bureau of Alcohol, Tobacco and Firearms, are searching for the man who is believed to have randomly murdered two men just 36 hours apart.
Douglass Watts, 73, was gunned down on a sidewalk in the 1400-block of West Sherwin on Sunday morning. Just a day later, 24-year-old Eliyahu Moscowitz was also shot in the head and left for dead on the pedestrian path in Loyola Park.
Watts and Moscowitz did not know each other, authorities said, but they were shot with the same gun.
"We all want answers," Steve Loskutov, Moscowitz's friend, told ABC7 News earlier this week. "We all want justice. It's sickening to think about it."
Chicago police shared about a minute of surveillance video of the suspect. At one point the masked man is seen jogging down an alley. In the video, the suspect appears to walk or run with his feet pointed outward.
WATCH: Surveillance video of Rogers Park murder suspect
Chicago police release video of Rogers Park murder suspect
It is believed that he lives in the neighborhood, and authorities hope his unique gait will help identify him.
On Thursday, the Jewish Federation of Metropolitan Chicago announced a $10,000 reward for information in connection with the murders. Cook County Crime Stoppers has also offered a $1,000 reward. The ATF's added $5,000 Saturday brings the total reward up to $16,000.
Anyone with information is asked to contact police.