Aiden Leos was fatally shot while strapped to his booster seat during the 21 May 2021 incident on the 55 Freeway in Orange County when his mother Joanna Cloonan reacted with a middle finger gesture after being cut off by another car.
Marcus Eriz, 26, has admitted firing a shot into the trunk of Ms Cloonan’s vehicle in police interviews but insisted he did not intend to harm anyone.
Mr Eriz was arrested after a two-week manhunt that attracted national headlines.
In an opening statement, District Attorney Daniel Feldman said the fatal shot pierced Aiden’s liver, lung and heart, according to the Associated Press.
Ms Cloonan heard her son say “ow”, pulled the car over on the freeway and tried to staunch the bleeding with the help of an off-duty police officer, Mr Feldman told the jury. Despite their efforts, Aiden died at the scene.
After the shooting, Mr Eriz stashed the vehicle in a relative’s garage and tried to change his appearance by shaving his head, according to prosecutors.
“This is not a road rage case,” Mr Feldman said. “This is an expression by Mr Eriz of cold indifference. This is an expression by Mr Eriz of his callous and total disregard for human life.”
When he was interviewed by police two weeks later he told them he grabbed the gun and fired the shot, knowing it was dangerous, Mr Feldman added.
Defence attorney Randall Bethune told the court that Mr Eriz did not mean to kill anyone and didn’t become aware of Aiden’s death until several days after the incident when a co-worker mentioned that his girlfriend's car matched a description of the one police were looking for.
“He had no hindsight, no clue as to the consequence of his actions in the moment,” Mr Bethune said, according to the Associated Press.
Mr Eriz has pleaded not guilty to murder and discharge of a gun into an occupied vehicle and faces up to 40 years in prison if convicted.
His girlfriend Wynne Lee has been charged with being an accessory after the fact and having a concealed firearm in the vehicle and will be tried separately.