A migrant from Guatemala has been arrested for allegedly lighting a sleeping subway rider on fire in Brooklyn on Sunday morning — then watching as his innocent victim burned to death in what the New York's top cop called “one of the most depraved crimes one person could possibly commit.

The "person of interest" was taken into custody hours after the attack while riding another train, according to NYPD Transit Chief Joseph Gulotta.

New York City police arrested and charged a man suspected to have set a woman on fire in the subway early Sunday and then watched from a bench as she became engulfed in flames and died.