It happened around 5:45 a.m. on Friday.
The NYPD responded to a call for an unconscious man on the southbound platform of the M/R line at the Grand Avenue-Newtown Station.
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Officers found the man unconscious and unresponsive with a stab wound to the upper chest.
EMS took him to NYC Health & Hospitals/Elmhurst but it was too late to save his life.
There are no arrests and the investigation remains ongoing, according to police.