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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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.