A man was killed on Christmas evening after a shooting broke out at an apartment complex in Aurora, according to the Aurora Police Department.

The fatal shooting happened just after 6:30 p.m. Saturday outside of the Chelsea Park Village Apartments at 86 N. Oakland St., near the Aurora Hills Golf Course, police said.

Police said the incident began when two men got into an argument outside of the apartment complex. During the argument, both men pulled out guns and one of the men shot the other.

The victim, a 35-year-old man, was taken to a hospital where he later died of his injuries, police said. The shooter, a 33-year-old man, stayed at the scene of the crime and is cooperating with investigators.

The victim and the shooter knew each other prior to the shooting, police said. It was unclear what their relationship was or what they were arguing about.

As of Sunday morning, the shooter had not been arrested. Police said they are working with witnesses to determine what led up to the shooting and who was the primary aggressor.

Anyone with information is asked to call Metro Denver Crime Stoppers at 720-913-7867. Tipsters can be anonymous and are eligible for a $2,000 reward for information leading to an arrest.

The Arapahoe County Coroner’s Office will release the identity of the victim in the coming days after his family is notified.