HOUSTON -- A psychiatrist testified on Tuesday that a man accused of killing a Houston police officer suffered from alcoholic withdrawals that contributed to the fatal crime, 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 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.

Jurors heard testimony that Quintero drank a case of beer every day -- the equivalent of 24 cans -- and that he was a lifelong alcoholic. However, defense attorneys said Quintero was not inebriated during the shooting, which led to even more problems with Quintero's mental state because of alcohol withdrawals.

Jurors were shown a diagram of a brain's anatomy. A neuro-psychologist and researcher testified that Quintero's brain scan showed damage to his frontal lobe, which controls his ability to reason.

Dr. Daniel Creson, a psychiatrist, testified that Quintero suffered a psychiatric crisis fueled by severe anxiety, alcohol withdrawal and brain damage when he shot Johnson.

Creson said that Quintero was unable to discern right from wrong.

Creson said Quintero told him, "I think if I had been drinking, I would not have been so scared and I would not have done what I did."

The psychologist was also on the stand for nearly three hours Monday. He told the jury about four other times Quintero was arrested on alcohol-related charges. He gave authorities his true name and was later deported to his home country of Mexico in 1999 after he was convicted of indecency with a child.

Quintero sneaked back into the United States, according to authorities. He was later hospitalized at Ben Taub Hospital with a self-inflicted gunshot wound to his abdomen. Testimony revealed that Quintero gave the hospital a fake name, Leonardo Lopez, during his stay there.

Also in the courtroom on Tuesday, HPD assistant chief Charles McClelland offered support to Johnson's widow and sent a message of appreciation to all officers.

"This is very, very dangerous work that we're doing. We're not playing games. (Officers) put their personal safety on the lines every day and every night," he said.

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 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.

Before the trial began, Quintero offered to plead guilty in exchange for a sentence of life in prison, but prosecutors rejected the offer because they are seeking the death penalty.

One of Quintero's defense attorneys was found in contempt of court before the trial resumed on Tuesday for not bringing the proper paperwork to the state to cross-examine Creson. The judge said she would decide the attorney's punishment, if any, after the trial ends.