A 21-year-old man was jailed on suspicion of murder Saturday in connection with the fatal shooting of a Navy man who stopped to assist a seemingly stranded motorist on Interstate 15, San Diego police said Sunday.

Brandon Acuna, who was taken into custody and questioned shortly after the shooting, was later arrested on suspicion of first-degree murder and burglary. San Diego police Lt. Anthony Dupree declined to specify Acuna's level of involvement in the killing, adding that others may have been involved in the Saturday shooting.

The victim, 21-year-old Curtis Adams, was with his girlfriend when they spotted a man standing next to a white vehicle on the shoulder of the freeway near Interstate 5 on-ramp about 2:20 a.m., Dupree said.

The couple pulled over to help. When Adams exited his vehicle, he was immediately shot.

The shooter got back in his vehicle and fled south.

Soon after, California Highway Patrol officers put out an alert that a similar vehicle was stopped on northbound I-5 near 32nd Street. A man was also seen walking away from the vehicle.

Officers found the man on Newton Street, later identified as Acuna, and he was taken into custody.

Investigators also suspect Acuna was involved in a second shooting that occurred about 10 minutes before the slaying of Adams. In that incident, police said a man was shot at after interrupting suspects who were breaking into his vehicle on Boundary Street in the community of Mount Hope.

Detectives are working to determine who else was involved in that incident, and everyone's level of involvement, including Acuna's.

This article is written by Lyndsay Winkley from The San Diego Union-Tribune and was legally licensed via the Tribune Content Agency through the NewsCred publisher network. Please direct all licensing questions to legal@newscred.com.