HOUSTON -- A man accused of shooting a Houston police officer to death will use the insanity defense in his case, KPRC Local 2 reported Thursday.

Attorneys for Juan Leonardo Quintero, 33, filed papers showing they will use the insanity defense.

Quintero is accused of shooting veteran Houston police officer Rodney Johnson to death in September 2006.

Prosecutor Denise Bradley said, "In order for a defendant to prevail on an insanity defense, they would have to show that the defendant had suffered from a mental disease or defect, some form of mental illness that would render them incapable of understanding that their conduct was wrong."

She said the defense does not change her preparation.

"I'm not surprised the defense would attempt to raise any type of defense," she said.

Quintero is accused of shooting Johnson four times in the head after Quintero was put in the back of a patrol car. Quintero faces a charge of capital murder of a police officer.

Pre-trial hearings are under way to certify experts expected to testify in the trial. The trial is expected to start soon.