Wednesday's ruling means that when he is sentenced in January, Sadowski will not be sent to a state mental hospital. He now faces a maximum of life in prison without parole.
He was convicted earlier this month of first-degree murder and carjacking for the 2005 death of LAX police officer Tommy Scott. Prosecutors say it all began when Sadowski carjacked a patrol car near the airport. Officer Scott held on and was decapitated when the car hit a fire hydrant.
Sadowski had pleaded not guilty by reason of insanity.
The Associated Press contributed to this report.