Police say 50-year-old Nathaniel Avinger intentionally set a fire inside a train at the 110th Street station in Harlem back in March.
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The fire killed 36-year-old MTA motorman Garrett Goble.
Avinger was questioned by police the day after the fire but was released.
Investigators say he was arrested this week for groping a subway conductor and that's when he made statements connecting him to the deadly fire.
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