CASTRO VALLEY (CBS SF) — The California Highway Patrol has arrested a 23-year-old Oakland man in a shooting on westbound I-580 in Castro Valley, but the case has an odd twist to it.

The CHP said officers responded to a call from service on westbound I-580, west of 150th Ave at around 12:40 p.m. on Tuesday.

Arriving officers found a vehicle with three occupants and the driver suffering from a back wound. After medical assistance was rendered, the detained the two passengers and the victim was transported to Highland Hospital suffering from critical injuries.

Investigators said one of the passengers, 23-year-old Antoine Robinson of Oakland, was found to be in possession of a firearm. One spent casing was located in the vehicle where Robinson had been sitting.

Additional evidence was located indicating Robinson had possessed a .40 caliber firearm.

During the interview of Robinson, the CHP said, he admitted to possessing the firearm and to firing the round that struck the victim.

Robinson was booked into Santa Rita Jail for a variety of charges, including assault with a deadly weapon and carrying a concealed weapon.