A 30-year-old man was killed on the New York City subway Monday after he started acting erratically and another passenger put him in a headlock, police say.

Police have yet to identify either man involved. The 30-year-old entered a northbound train at roughly 2:30 p.m. and began making threats against other passengers. Another male passenger, 24, stepped in and put the other man in a headlock until he was unconscious. An EMS officer who responded could not revive the man.

Police say the deceased man had a long criminal record, including convictions for assault, disorderly conduct and fare beating, according to the New York Post.

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Scene on a NYC subway

Police have yet to identify a man who was killed in the NYC subway Monday after threatening other passengers. Officers are working to notify his family. (Paul Martinka)

Unconscious man on a subway

A 24-year-old man choked another man, 30, unconscious with a chokehold Monday after the older man began acting erratically and making threats. (Paul Martinka)

Police roping off a subway

Police cordoned off the area around the older man, who was pronounced dead in a subway station. Police released the 24-year-old who placed the man in a chokehold. (Paul Martinka)

man lying on the ground in a subway

NYPD officers were unable to revive a 30-year-old man who was put in a chokehold after threatening other passengers on a New York City subway. (Paul Martinka)

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The 24-year-old, who has not been identified, was released without charges Tuesday. The man who died has also not been identified because police are working to notify his family.