According to Valdivia, there was a bullet hole in the silver Chevrolet and the six-year-old appeared to have been shot in the back.
Police believe the boy's mother, who was driving the auto, was the target of road rage, CHP spokesperson Florentino Olivera said.
'She had blood on her clothes and he started turning blue and that's when the ambulance took him and that was the last time my mom saw him alive, ' said Alexis Cloonan, the boy's sister, during a tearful family press conference on Friday.More news: Top Republican senators divided over January 6 commission
The boy was struck from behind when a single round passed through the trunk of the vehicle, the Los Angeles Times reported.
The boy was transported to a local hospital, where he was pronounced dead, Olivera said. The male passenger is believed to have fired the fatal shot while his female accomplice was driving the vehicle, believed to be a white Volkswagen wagon sedan.
The woman said she steered her auto to the right and noticed there was a man and woman inside the white sedan, and they pulled behind her and someone fired a gun.
Other motorists stopped to help, including an off-duty police officer who performed CPR on the victim until paramedics arrived.
CBS Los Angeles reported that there have been almost a dozen pellet and BB gun shootings on freeways across Los Angeles, Orange and Riverside counties over the past three weeks, but Olivera said Friday's road-rage killing was unrelated to those earlier incidents.More news: Israel steps up assaults in Gaza with shells, airstrikes
The 55 freeway was shut down for hours as investigators combed the lanes for possible evidence.
Such shootings aren't unprecedented on California's busy roadways.
The suspected shooter remains at large and officers are looking for a white sedan, Olivera said.
Officer Florentino Olivera from the California Highway Patrol urged witnesses to come forward with any information they might have.More news: CDC To Update Guidelines Allowing Vaccinated People to Go Maskless Indoors