The shooting happened on a BX36 bus on White Plains Road and East Tremont Avenue just before 3 p.m.
It appears the victim, Jonathan Pettigrew, told the gunman to stop yelling on his cellphone.
An argument ensued and the suspect, described as a young man in his teens, shot Pettigrew in the abdomen.
Pettigrew was taken to Jacobi Hospital where he was pronounced dead.
"I just saw a whole bunch of commotion, whole bunch of people outside, where the bus is parked is actually not a bus stop so that's how it caught my attention," said witness Destiny Flores. "A whole bunch of people when we went outside., the cops were already outside. We thought maybe somebody was hit by the bus until one of the kids on the bus came across the street and let us know that it was a shooting."
The MTA says this is the first homicide on a bus this year.
It's unclear if the bus camera caught the shooting. Police have not yet released any images of the gunman.
No arrests have been made and the investigation is ongoing.
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