The woman hasn't been formally charged yet but police said the woman in custody "made statements implicating herself."
Sunando Sen, 26, died Thursday after he was pushed onto the tracks by an unidentified woman as a train entered the platform. Witnesses said the woman who fled the scene after the attack was mumbling and cursing to herself before she knocked Sen on the tracks.
Further details on how police managed to identify the suspect in Sen's death were not immediately available but investigators had been checking homeless shelters and psychiatric units.
Witnesses said Sen had not interacted with the woman before he was pushed. The suspect's name will not be released until she is formally charged. Police said they were arranging for witnesses to positively identify the woman in custody as the attacker.
The attack marked the second New York City subway fatality push in a month. A homeless man is currently awaiting trial for murder after he allegedly pushed a man onto the subway tracks on Dec. 3.
There are no protective barriers in place along New York City's subway platforms to prevent riders from getting hit by trains. According to the Metropolitan Transportation Authority, 54 people were killed on the New York City tracks in 2012. Transit officials are considering installing sliding doors.
The Associated Press contributed to this report.