At age 12, Jorge Lira Garcia was gang-raped by a group of men in a bar in Mexico.

That severe sexual trauma as a child contributed to a chronic post-traumatic stress disorder that prevented Garcia, 26, from acting rationally the afternoon Erika Arroyo walked into his apartment, according to a psychologist who testified on Garcia's behalf Tuesday."At the time he had Erika by the throat, he was responding to internal cues due to irrationally perceived threats as a result of his sexual abuse as a child," said Dr. Mercedes Reisinger-Marshall, a clinical child and forensic psychologist hired by the state to conduct a psychological evaluation of Garcia.

"He did not intend to kill her," she said. "At the moment that he was strangling (Arroyo) he was not able to form the requisite intent in order to form a knowing and purposeful action."

Garcia is on trial this week in the Aug. 25, 1997, slaying of Arroyo, 7, who was strangled and raped. Charged with capital murder, Garcia could be sentenced to die if convicted.

After the hearing, Reisinger-Marshall said she felt awkward testifying for the defense in this case because she commonly testifies for prosecutors. However, in her eight years as a forensic psychologist conducting from 10 to 15 evaluations a month for the Board of Pardons, she has not seen an accused felon with a worse case of post-traumatic stress syndrome, she said.

"He was a time bomb," she said. "This is one of the most severe cases that I've ever seen."

During several interviews with Garcia, Reisinger-Marshall learned of two sexual assaults he experienced as a child. The first, a sexual assault by an adult neighbor, took place when he was 8 years old. But it was the second, at 12, that left him severely traumatized, she testified.

He was out drinking in a bar with a group of adult men when they began to touch each other inappropriately, she said. Garcia wanted to leave but first went to the bathroom. The men followed him and raped him.

Garcia does not remember the actual assault. But he has a vivid memory of running home with his pants down and screaming. He felt the screams were coming from someone else, Reisinger-Marshall said.

When he got home, he found a gun and tried to kill himself but his father stopped him, she said. After that, Garcia began to drink excessively and to use drugs.

Garcia's rape became widely known throughout his small town, in the state of Michoacan, Mexico, she said. About the same time, an explosive device accidentally exploded near his head and he has since experienced blackouts and memory loss. He quit school that year.

Although family members say Garcia is not violent, they report he becomes significantly angry whenever he hears loud noises.

"He cannot tolerate any type of loud voice" possibly because it may be a cue that unconsciously reminds him of the gang-rape, Reisinger-Marshall said. "When children are sexually traumatized that severely, anything that will remind them . . . will trigger that memory."

When Erika Arroyo began to scream after he tried to make her leave his apartment, the screams may have triggered the memory of his rape.

Prosecutor Bill Danes countered Reisinger-Marshall's testimony by pointing out that Garcia had apparently known what he was doing because he tried to hide the body after the attack in an alley behind the house.

However, at the moment Garcia grabbed Arroyo by the neck, "he was not aware that this was a little girl at all," Reisinger-Marshall said. He was instead responding to a perceived threat.

Testimony in the case is expected to continue Wednesday with closing arguments expected on Thursday. The case could go to the jury as early as Friday.