Two teens opened fire on a barbecue at an Auburn apartment complex late Sunday afternoon, killing one youth and seriously injuring two other people, Auburn police said.

Four people are in custody, but one of the teens whom police say opened fire, 16-year-old James Anthony Mills, was still on the run as of Monday afternoon, police said.

Mills, a Kent resident, is wanted for second-degree murder. He is 5 feet 4 inches tall, 115 pounds with black hair and brown eyes. He is considered armed and dangerous.

The Aspen Meadows Apartments in the 400 block of 21st Street Southeast remained on lockdown until police finished processing the scene at 6 a.m. Monday.

According to Auburn police, a 17-year-old boy was hosting the crowded barbecue. At some point, police say, Mills showed up with a group of friends, and he and the 17-year-old began to argue in the courtyard of the apartment complex.

“The argument that started was based on the girlfriend of one of two individuals,” said Auburn Police Commander Mike Hirman. “We don’t know exactly how it happened, but it escalated from there into a physical fight.”

Without warning, Mills and another person allegedly pulled out guns and began shooting into the crowd. Police say Mills shot at the 17-year-old multiple times, striking him once. The youth died of his injuries at the scene. Two other people were wounded, Hirman said.

Several people called 911 as Mills and his friends fled, Mills allegedly firing off random shots as he ran. Police from surrounding jurisdictions responded, and patrol cars surrounded the scene within minutes.

“We were notified of the fight while en route down there, then another dispatch indicated it had escalated to a shooting. By the time we arrived, three individuals had been hit, and one was pronounced dead at the scene,” Hirman said.

Police arrested four people — including one of the suspected shooters — but Mills got away.

“We know there were at least two shooters, according to the information we have so far,” Hirman said.

Medics transferred two people to Harborview, where they remain in serious condition.

An Auburn officer tried to arrest one of the fleeing suspects but fell and injured his back. He is expected to survive.