EAST BOSTON — A 15-year-old boy was arrested Tuesday night after he and another suspect wearing ski masks ambushed a man on a residential street, stabbed him, and tried to steal his scooter, Boston police said.

The attack unfolded just after 10 p.m. on Paris Street in East Boston when two males in ski masks approached the victim and demanded his personal belongings, including his scooter. When he refused, the two suspects attacked him, stabbing him as he tried to flee toward Sumner Street, police said.

A passing driver saw the attack, jumped out of his car, and managed to wrestle a knife away from one of the suspects before discarding it. A second witness reported seeing the suspects making "jabbing gestures" toward the victim's body.

Both suspects fled. But in a move that could charitably be described as not his brightest, one of them came back to the scene to look for his cell phone.

Officers had already recovered two knives wrapped together in duct tape and a cell phone from a handicap ramp at the intersection of Sumner and Paris streets. When the suspect returned asking about his phone, officers identified him and took him into custody. A ski mask was found among his possessions during booking.

The victim was transported to a local hospital with non-life-threatening injuries.

The 15-year-old, a Boston resident whose name was not released due to his age, was charged with aggravated assault and armed and masked robbery. He is expected to be arraigned in Suffolk County Juvenile Court.

The second suspect remains at large.