WEST PALM BEACH — The jury heard from Nathaniel Brazill for the first time Monday, but the boy, speaking during a videotaped police interview, said nothing that would explain why he walked into school with a gun and shot his seventh-grade English teacher.

A television facing the jury box threw a soft light onto the panel as they attentively watched the videotape in the darkened courtroom and occasionally glanced at transcripts of the interview. In its fourth, and second-to-last, day of testimony, the prosecution presented the tape as evidence of Brazill's confession to the killing.

Brazill, now 14, and his lawyers moved from the defense table to a position by the witness stand where they could see the screen. Consequently, the jurors could easily slide their glance from the boy's image on the screen to Brazill himself, sitting docilely in a sky blue shirt and black slacks.

Although composed in the courtroom, the defendant seemed bewildered and unnerved and on the videotape.

"I think I pulled out the gun, I was like shaking a lot. I could hardly hold the gun. And I was afraid to drop, drop it 'cause I didn't know what was gonna happen if I would of dropped it. And so it all just went from there," the boy recounted to detectives.

Questioned several times about why he shot Barry Grunow, 35, and how the shooting occurred, Brazill never offered an explanation, repeating that he had been angry and that he did not know what had happened.

The boy finally began crying during the interview when his mother, Polly Powell, arrived. Her scarlet t-shirt — showing a picture of two hands clasping above the word "together" — stood out dramatically against the white walls and bland brown furniture of the interrogation room.

"Nate. Come on. If I taught you anything didn't I teach you to think first?" she implored, and later asked, "Why Nate? You know better than that. You know what guns do. Oh God."

Eventually the police left the two alone, but neither talked much. The two wept and covered their faces at one point, and Powell wiped tears from both her own eyes and those of her son.

Brazill faces life in prison without parole if convicted of first-degree murder for killing Grunow, one of his favorite teachers, on May 26, 2000, the last day of school before summer vacation for Lake Worth Community Middle School.

Sent home early from school and upset that he would not be able to see a girl he liked, Brazill, a successful student well-liked by teachers and classmates, returned to school with a gun and demanded that Grunow release her from his class. When the teacher refused, the boy drew his gun and, after further demands were denied, shot him in the head. The prosecution says the shooting was premeditated, while the defense claims that the gun went off accidentally.

With so much debate over how the shooting occurred, the firearm itself is a central piece of evidence. A small semiautomatic handgun made by Raven Arms, the weapon is generally considered to be of poor quality. Both sides called experts to testify about how well the gun worked.

Prosecutor Marc Shiner put two witnesses on the stand who testified that the gun worked properly during tests.

"There's no reason for the gun to go off without pulling the trigger or some kind of force being applied to it," said Curtis Bartlett, chief of firearm technology for the Bureau of Alcohol, Tobacco and Firearms.

Carlos Rosati, a firearms and tool mark analyst for the FBI, agreed with this assessment and added, "The safety works normally, as the manufacturer intended it."

The defense's firearm expert testified, however, that the gun might discharge accidentally. Because he could not come to court at any other time, Lama Martin, a weapons tester who used to work for the government but now has a private practice, testified Monday rather than during the defense's case.

Martin said that the type of gun Brazill used, with its light "trigger pull," was prone to going off unintentionally.

"I have been involved in investigating many accidents with [similar] semiautomatics when triggers were pulled accidentally in periods of high excitement or stress," he said.

To further bolster this claim, Martin described how the New York Police Department had once issued weapons with similarly light trigger pulls, only to recall them after a rash of unintentional shootings by officers.

The defense expert also said that the gun's safety mechanism was poorly designed and could have been switched off when the boy drew the weapon from his pocket. "You can 'wipe the safety off' by pulling it out of a pocket or holster," he said. "[This gun] is prone to being wiped off."

The prosecution also called Dr. Charles Siebert, the medical examiner who performed Grunow's autopsy. He testified that the bullet passed through the teacher's brain and deflected off the back of his skull, coming forward again before stopping. Siebert also said that Grunow died nearly instantly and that no medical intervention could have saved him.

Speculation had arisen Friday that a mystery witness who had talked with Brazill in jail might testify for the prosecution. But the prosecutor said Monday that the source turned out to lack credibility and would not take the stand, shortening the prosecution's case somewhat.

The jury will finish watching the tape of Brazill's police interview Tuesday morning and, after the testimony of three more witnesses, Shiner plans to rest his case near midday.

The trial is being aired live on Court TV.