The suspected shooter, 24-year-old Marcus Anthony Eriz and his girlfriend, 23-year-old Wynn Lee, appeared in court in Santa Ana Friday morning.
Eriz, who was previously being held on $2 million, was ordered to remain jailed without bail. Judge Larry Yellin said Eriz's alleged actions during the shooting and after, with prosecutors alleging he wielded a gun at another motorists days later, were "alarming."
Bail for Lee, who is charged as an alleged accessory in the shooting death of the boy, will remain at $500,000, but Orange County Superior Court Judge Larry Yellin has asked that Lee undergo a background review ahead of another bail hearing set for next Friday.
A pretrial hearing was scheduled for Aug. 27.
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According to court documents, Eriz allegedly pulled out a gun and fired at a car on the 55 Freeway in Orange that was being driven by a woman who made a rude gesture toward him on a freeway while he was on his way to work on May 21.
The shot killed Aiden while he sat in a booster seat in the back of his mother's car on his way to kindergarten, prosecutors have said.
Days later, a co-worker told Eriz that authorities were looking for a car similar to the one he used with Lee, who since has been charged with being an accessory after the fact, the court filing said.
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Eriz then hid the car in a relative's garage and instead started using a red truck, shaved his beard and began pulling back his hair, prosecutors said in the document.
Days after Aiden was killed, prosecutors said Eriz brandished a gun at another driver on the freeway.
"This brazen act of threatening other commuters with a loaded firearm shows this Court that the Defendant cannot control his emotions and the smallest event can set him into a deathly rage," prosecutor Whitney Bokosky wrote in the filing.
The Associated Press contributed to this report.