Meanwhile, a makeshift memorial for the father, 35-year-old Luis Mendoza, continued to grow Monday outside the family's La Puente home.
"The family, they're in shock," a family friend, who gave his name only as Giovani, told ABC7. "It's still unreal. It's hard for them to believe it still."
The CHP was summoned to a multi-vehicle crash at 12:28 p.m. Saturday on the eastbound 60 Freeway, just east of Crossroads Parkway, the California Highway Patrol said.
Arriving officers found a white Chevrolet Avalanche pickup truck with extensive damage from colliding with a white Kia and a concrete retaining wall, the CHP said.
The three victims were taken to Los Angeles County-USC Medical Center, where Mendoza was pronounced dead. The father is survived by his wife and five children.
The 13-year-old suffered major head injuries and the 16-year-old suffered minor injuries, the CHP said.
Witnesses told the CHP the front passenger of a silver or gray compact vehicle in the HOV lane pointed a handgun out of a passenger-side window and fired several shots at Mendoza's truck, causing him to lose control and slam into the Kia and the retaining wall. The sole occupant of the Kia was not hurt.
"I heard it was road rage," Giovani said. "The two boys, they seen everything, witnessed everything, remember everything."
Authorities have not confirmed a motive for the shooting, which remains under investigation.
A description of the shooter, who remained at large, was not available.
"If anybody has any clue to the suspect, the suspect's license plate -- we know it's a gray sedan, Corolla or Camry," Giovani said. "But that information only goes so far."
Anyone with information about the shooting is urged to call the CHP at (323) 259-3200 or CHP Major Crimes at (323) 644-9550.
A GoFundMe page has been created to help pay for Luis Mendoza's funeral.