BALTIMORE (AP) _ When the milk carton flew through Northern High School's cafeteria and hit one of the Bella Vista Boys, the neighborhood gang blamed Wayne Martin Rabb.

By all accounts, the shy 15-year-old student had nothing to do with it. But he was stomped and beaten unconscious that same day.

That wasn't the end of it.

Last week, Rabb _ armed with a baseball bat, police say _ apparently took the schoolyard squabble to the streets, where he was gunned down in the middle of the afternoon in front of more than a dozen horrified onlookers.

On Thursday, the day of Rabb's funeral, police arrested 16-year-old Marcus Chambers, a former Northern High student, on murder charges.

Until Jan. 9, Rabb had not had any problems at Northern, a school notorious for its violence. Principal Alice Morgan-Brown made headlines in November when she suspended three-quarters of the school's 1,800 students for refusing to report to homeroom to get their report cards. She later rescinded the suspensions.

``As far I knew him, he was a quiet kid,'' Ms. Morgan-Brown said Thursday. ``We don't know what happened that day exactly. But somehow some milk got tossed on one of the students, and he was blamed.''

The Bella Vista Boys _ named, in a fashion, after the Baltimore neighborhood Belle Vista _ didn't just blame Rabb, they ``banked'' him, or ganged up on him to teach him a lesson.

Witnesses said as many as 15 students jumped Rabb after school and stomped on him until he lost consciousness. He stayed home for a week. Three boys were suspended for the rest of the year. Only one was charged.

``I don't think there is anything else we could have done,'' Ms. Morgan-Brown said. The school has at least 15 security guards and three police officers on the grounds during the day, she said.

Rabb asked his mother, Charlene Rabb, to apply for a transfer to another high school, but she didn't push for it. ``I thought there was time,'' she said.

Even after the beating, Rabb wasn't afraid to go back to school, said Rabb's cousin, Chanta Doughty.

``He didn't understand why they was beating him up already, but he thought that was it,'' she said. ``He didn't give another thought about it.''

But when Rabb came home Feb. 5 with a bloody lip, his mother told him to stay home until the transfer came through.

On Feb. 6 he was dead, three days before he was supposed to testify against Dominic Stokes, 18, who was charged in the schoolyard assault.

Rabb's 21-year-old brother, Carey Scott, said it was his idea to approach the group of boys his brother said had been bothering him. But police said Rabb went looking for trouble.

``Rabb was with a bunch of people and he was carrying a baseball bat when he approached the group,'' Detective Donald Kramer said.

Scott said no one had a bat. He thought he could warn the group to stay away from his little brother.

``I know Marty was tired of it, tired of being pushed around,'' Scott said. ``We went over there and that's when one of them pulled out the gun. No one said nothing, not a word. Marty, he was just frozen.

``When the guy cocked back the gun, put a bullet in the chamber, I just yelled `Marty! Run!' But when he started running, the boy just shot him. When Marty fell, he came over on top of him and shot him again.''