Less than four years ago, Donald Johnson was cited for heroism after he rescued a family from a fire. Last week, police fatally shot the teenager after he took a Greyhound bus for a joy ride.

Police maintain they shot at the bus, killing Johnson, because he was endangering the lives of others by refusing to stop driving erratically through a Boston neighborhood late at night. And city officials, in preliminary findings, say the shooting was justified.But his mother, Betty Johnson, a longtime community activist, and other black leaders claim that police overreacted, shooting someone who was unarmed and had no criminal background.

Mrs. Johnson, 48, is unable to explain why her son, a junior in high school who turned 19 the day before he died, took the bus on Jan. 31.