Marcus Anthony Eriz, 24, has now been charged with murder and discharge of a gun into an occupied vehicle, authorities have confirmed.
His girlfriend, Wynne Lee, 23, has been charged with accessory after the fact, a felony, for concealing the shooting, and a misdemeanor count of having a concealed firearm in a vehicle.
They had originally both been expected to be arraigned in a California courtroom on Tuesday but this was eventually pushed back to 18 June.
Mr Eriz mean could face 40 years to life in prison if convicted, while Ms Lee faces up to three years behind bars if convicted and bail has initially been set at $1m for each suspect, although that figure could change at their arraignment.
Investigators arrested them at their home in Costa Mesa, California, on Sunday, two weeks after Aiden’s killing.
His mother, Joanna Cloonan, told another motorist at the scene that she and her son ere driving in the carpool lane when another motorists cut them off as she tried to switch lanes.
She said she made a rude gesture at the people in the other car and continued to try and exit the 55 freeway.
Investigators believe that Ms Lee allegedly brought the car behind Ms Cloonan’s vehicle and Mr Eriz allegedly fired the shot that killed Aiden.
“Mr Eriz, if he is convicted on any or both charges, will spend a significant portion of his adult life in prison,” said Orange County District Attorney Todd Spitzer on Tuesday.
“We would not file these charges unless we could prove them beyond a reasonable doubt,” he added, calling them “rock solid.”
California Highway Patrol officials announced on Monday that they had found the gun and the car used in the shooting.
Mr Eriz formerly worked at an autobody shop and has reportedly posted pictures of himself shooting weapons at a gun range on social media.
“It could’ve happened to any one of us,” said Mr Spitzer on Monday.
“We all drive the freeways of Southern California. We’ve all gotten upset at other motorists, other motorists have gotten upset at us. I’ve thrown some gestures about myself.
“But it’s never come to a situation of violence and certainly not in my realm or your realm, to the loss of a life.”