An NYPD spokesman said Saturday that detectives had questioned a woman and that she had "made statements implicating herself" in the Thursday night killing.
Authorities didn't immediately name the woman.
Victim Sunando Sen died Thursday night when a woman who had been muttering to herself on a train platform in Queens suddenly knocked him on the tracks as a train entered the station.
The woman fled after the attack. Police had released security camera video showing her running from the station.