Police say the incident happened around 4:30 a.m. near Essex Street by the Williamsburg Bridge southbound J train.
When officers arrived, they found a 32-year-old man lying on the tracks, under the train, unconscious and unresponsive.
EMS responded and pronounced the victim dead at the scene.
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An investigation revealed that the man was seen riding on top of the train as it traveled.
The man lost his footing and then fell from the train to the tracks below and was struck by the train.
Police say there were no other injuries.
The investigation is ongoing.
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