A 14-year-old pointed a handgun at his 9-year-old brother's chest from two to three feet away, and thinking the gun was unloaded, pulled the trigger, mortally wounding the younger boy, a prosecutor said Monday in court.

Juanly Pena was being held on $50,000 bail after pleading not guilty to manslaughter and unlawful possession of a firearm in connection with the Feb. 7 death of his brother, Janmarcos. The shooting occurred on a school day in their home in Boston's Dorchester neighborhood, while their mother was outside warming up the family van.

The older boy was indicted by a grand jury earlier this month as a youthful offender, opening court proceedings to the public and subjecting the suspect to possible punishment as an adult. A manslaughter conviction carries a sentence of up to 20 years in prison.

Exactly how the boy got a hold of the gun remains under investigation.

"The evidence does not suggest that the defendant found a handgun and accidentally shot someone while playing with it," Suffolk District Attorney Daniel Conley said. "It suggests that the defendant procured the weapon on his own initiative and, though apparently believing it to be unloaded, pulled the trigger while it was pointed at his brother."

Juanly Pena had stopped going to school after he was arrested for fighting, prosecutor Ian Polumbaum said in court. His younger brother had stayed home to help his mother, who was trying to get home-schooling for the 14-year-old. Their 18-year-old sister was also home.

The older boy told police he thought the gun was unloaded because he had removed the magazine, but there was still a round in the chamber when he pointed the gun at Janmarcos.

"He never had a chance," Polumbaum said.

After the shooting, Juanly Pena started to call 911 but instead told his sister to call. He then left the house with the gun but was stopped nearby by police, still carrying the gun, authorities said.

The judge said if Pena makes bail, he is to be released to his mother, with electronic monitoring, and remain under house arrest except to attend school.

The boy's lawyer, Michael Doolin, did not contest the bail. The boy has the support of family but remains scared, Doolin said.

He is due back in court on May 27.