HOUSTON -- Defense attorneys tried to convince a jury Friday that a man was insane when he fatally shot a Houston police officer, KPRC Local 2 reported.

Officer Rodney Johnson was shot in his patrol car on Sept. 21, 2006, after a traffic stop in southeast Houston.

Juan Leonardo Quintero, 33, has been charged with capital murder of a police officer. He has pleaded not guilty by reason of insanity because a childhood injury left him with brain damage that made him paranoid and unable to accurately assess situations, according to his attorney.

A licensed forensics psychologist who has not examined nor met Quintero was the first witness to take the stand Friday. He is an expert witness being paid $400 per hour.

The psychologist testified about how a person reacts in a situation they perceive is threatening. Defense attorneys hope his testimony will prove that Quintero's has a history of mental and emotional problems and his actions were the result of a high stress and traumatic event.

Quintero told police in a videotaped statement that he killed Rodney Johnson because he was being given a ticket for driving without a license after he was stopped on suspicion of speeding.

Police said Quintero shot Rodney Johnson after Quintero was put in the back of a patrol car during a traffic stop in southeast Houston. Investigators said Quintero used a 9 mm handgun he had hidden in his waistband.

Quintero is a Mexican citizen who was deported in 1999 after being convicted of indecency with a child, but sneaked back into the country, according to authorities.

A large group of uniformed police officers have been in the courtroom throughout the trial.