OCEANSIDE, Calif. -- A 17-year-old boy was in custody Monday facing a murder charge in connection with the shooting death of his brother-in-law at the victim's North County apartment, police reported.

Officers responding to reports of gunfire in the 1200 block of South El Camino Real in Oceanside found Hector Nava, 26, gravely wounded at his rental residence shortly before 9:30 p.m. Sunday, Sgt. Kelan Poorman said.

Nava, a service station cashier and father of a 10-month-old child, died as medics were preparing to airlift him to a trauma center, Poorman said.

Homicide detectives went to the scene and interviewed the victim's wife and her teenage brother, then arrested the boy on suspicion of murder.

The motive for the slaying remains unclear, according to Poorman.

"Detectives are still investigating the story told to them to determine the reason for the shooting," the sergeant said.

The suspect, whose name was withheld because he is a minor, was booked into juvenile hall.