WEST PALM BEACH, Fla. — During a withering cross-examination, Nathaniel Brazill said he could not explain how he unintentionally shot Barry Grunow, his seventh-grade English teacher, although he admitted pulling the trigger.

The 14-year-old Brazill remained composed under an intense barrage of questions from prosecutor Marc Shiner, but he made several crucial admissions that contradicted testimony he gave Tuesday.

The prosecutor began his cross-examination by dramatically giving Brazill the gun he used to kill Grunow and asking him to demonstrate to the jury how the shooting occurred.

"Can you show us how it can go off unintentionally?" Shiner asked.

"Not really," Brazill responded, seeming confused by the question.

"You can't answer how it went off unintentionally?" the prosecutor prodded again.

"No," the boy answered.

Brazill is being tried in an adult court for first-degree murder. He faces life in prison without parole if convicted of murdering Grunow on the threshold of his classroom last May 26, 2000. The defense claims that the boy shot Grunow by accident while trying to scare the teacher into letting him talk to two girls in the class.

The prosecution continued to poke holes in Brazill's story throughout the morning session. On several occasions, the boy remembered events that he had denied knowledge of when answering questions from defense lawyer Robert Udell.

Brazill had testified that he did not remember questions asked of him by friend Tiffany Jenkins when he showed her his gun three days before the shooting. But under cross-examination he recalled her asking if he would ever use it to kill anyone.

The boy admitted mentioning that he might kill Jenkins' cousin, but maintained that it was a joke.

Brazill also acknowledged that, contrary to his testimony yesterday, he spoke with a student on the day of the shooting and told her that he was going home to get a gun to kill a school guidance counselor.

"How do you remember that now?" Shiner asked.

"You just refreshed my memory," the boy answered.

During Brazill's testimony, Shiner hung a large piece of paper on an easel between the witness stand and the jury box, wrote on it with a marker: "Brazill Can’t Remember." Through the course of the boy's testimony, the prosecutor added several items under this heading. Brazill said he could not remember talking to neighborhood teen Brendan Spann, who testified the boy asked him for the gun and said he was going to "f*** up the school." In addition, Brazill also denied speaking to student Jules Noel just before entering the school with a gun. Noel testified that the defendant warned him "you better get out of here."

Shiner also questioned the boy’s truthfulness and his lack of emotion on the stand. "You can sit here in this courtroom in front of lots of people, with television cameras, a Circuit Court judge and lawyers, and you don’t even look nervous," he said.

Brazill did begin crying at one point in his testimony when Shiner pressed him about the shooting itself, asking him what happened once he pulled the trigger.

"What do you think happened?" Brazill replied, covering his face with his hand and later wiping his eyes with tissue.

"Are you happy I won’t ask you any more questions?" the prosecutor asked at the end of his cross-examination.

"Yes," the boy replied.

After Brazill's testimony, Udell called three more witnesses, two of whom said that Brazill had changed remarkably since the shooting.

"He doesn't look himself. He looks like he's lost his sense of humor. He looks sad. He looks resigned. He looks despondent," said Sharon Purce, Brazill's sixth-grade English teacher, with whom the boy had remained close.

Theresa Young, a Lake Worth resident who knew Brazill from her work at a neighborhood youth center, affirmed that the boy had a reputation for truthfulness within the community.

"He's grown up. He's bigger," she said of Brazill, later adding, "He was a good kid. He never bothered anybody and nobody ever bothered him."

The defense will continue its case Wednesday afternoon.

The trial is being aired live on Court TV.