BALTIMORE (AP) _ The last time Edna Munford saw her son William alive, she was chastising him for not heeding her warning to stop feeding the pit bull puppy he had found on the street.

Then, as he went outside to play Wednesday afternoon, she told the 10-year- old not to touch the loaded sawed-off shotgun he and his friend Darrell had found in an alley near the Munfords' home.

That warning also went unheeded.

According to police, William and Darrell sat on a neighbor's doorstep and marveled over the short barrel and stock. Then, police said, Darrell pointed the gun at William and pulled the trigger.

William died at the scene, and 10-year-old Darrell was arrested on charges including first-degree murder. Police did not release Darrell's last name because he is a juvenile.

Family and neighbors said Thursday they can't believe the killing was intentional, but police said their interviews with Darrell convinced them the boy knew what he was doing.

Ms. Munford, 35, said she had recently moved her family to what she thought was a safer neighborhood. There were still some problems with crime and drugs in the area, though, so finding a loaded gun in the alley didn't shock her.

''I didn't think to call the police,'' she said.

Before the start of school Thursday morning, William's classmates at the Robert W. Coleman Elementary School gathered in the auditorium to talk with counselors and among themselves about the death.

School officials said the incident was a reminder that they must warn children against dangers that only a few years ago were not a concern. William is the third Baltimore boy under 15 to be killed with a gun this month.

His friends stood in turn and described him as a popular, athletic boy who liked eating sugar-candy out of a straw and could do a standing flip. He won a math achievement award last week.

Assistant Principal Sandra Graves recalled that hours before the shooting, William came by her office to pick up a pencil he had left with her for safekeeping.

''He didn't look for trouble,'' Ms. Graves said. ''He could make you laugh, and he had the biggest cheerful smile, with big, bright eyes. This was just one of those things. He was aware, but he just got caught up in that situation.''

Neighbor Edward Muse said the two boys were both easygoing kids.

''All kids find things and play with them,'' Muse said. ''I'm quite sure he (Darrell) didn't have anything against Will because they were the best of friends. When you saw one, you saw the other.''

Ms. Munford refused to respond directly when asked if she thought the shooting was deliberate. ''As far as I know they were friends,'' she said. ''They had fights like little kids have, and then they made up.''