Police say Jerome Isaac was arrested Sunday and had burns on his face. It wasn't clear if he had a lawyer. Police say he said she owed him $2,000.
Deloris Gillespie died Saturday in the small elevator of her Brooklyn apartment building.
Surveillance video shows a man looking like an exterminator with a canister sprayer, white gloves and a dust mask. The sprayer was full of flammable liquid.
He sprays the woman as she cowers, then tosses a Molotov cocktail into the elevator.