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

Four people were taken into custody that day, but one of the teens who opened fire, 16-year-old James Anthony Mills of Kent, was arrested Monday night at a relative’s home in Kent and booked into the King County Juvenile Detention for investigation of murder, according to Auburn Police Commander Mike Hirman.

Prosecutors formally charged Mills as an adult with 2nd-degree murder Wednesday afternoon. He is scheduled to be arraigned June 6.The Associated Press identified the victim as 17-year-old Adrian Wilson. The victim’s father, 46-year-old Gabriel Wilson, has been charged with first-degree assault for firing shots during the melee.

Detectives are following leads to recover the weapon used in the shooting, as well as other evidence.

The Aspen Meadows Apartments remained on lockdown until police had finished processing the scene by 6 a.m. Monday.

One of the first officers to arrive at the scene in the 400 block of 21st Street Southeast injured himself while making an arrest.

According to Auburn police, Adrian Wilson was hosting the crowded barbecue. At some point, Mills showed up with a group of friends. He and the 17-year-old began to argue.

“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, killing the 17-year-old and wounding two other people, Hirman said. Several people called 911 as Mills and his friends fled, Mills 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.

Medics transferred two people to Harborview, where they remain in serious condition. As an Auburn officer tried to arrest one of the fleeing suspects, the officer fell and injured his back. He is expected to survive.