The suspect, a man in his 20s, allegedly robbed another straphanger at knifepoint on a train Thursday morning.
He stole about $150 cash from his victim and fled through the train, police said.
The quick thinking victim called 911, and police officers met him at the World Trade Center station.
The victim pointed out his suspect to police, who ordered the mugger not to move.
Instead, the suspect fled towards a northbound E train, which was pulling out of the station.
Police said he tried to jump from the platform to the train, attempting to land in the space between train cars.
He lost his balance and fell under the moving train. He was rushed to New York Downtown Hospital, where he was pronounced dead.
Detectives believe the mugger attempted another armed robbery earlier in the evening in the area of Pace University.