The 47-year-old man, who hasn't been charged, said he had started a fire, said New York Police Department spokesman Paul Browne. The man's identity hasn't been released.
Deloris Gillespie, 64, was ambushed in the elevator of her Brooklyn apartment building on Saturday afternoon, doused with an accelerant and set afire with a Molotov cocktail, Browne said. The suspect had been waiting for her when the elevator doors opened to the fifth floor of her apartment building in Prospect Heights, police said.
"It was apparent he knew she was on the elevator," he said Saturday.
The attack happened shortly after 4 p.m., lasted about a minute and was recorded by two video cameras, including one inside the small elevator.
The video showed the elevator doors opening to the floor where Gillespie's apartment was located and the assailant stepping in and spraying her, Browne said.
Gillespie, who had grocery bags in her arms, turned about 180 degrees and then crouched in an attempt to protect herself, he said. But the man sprayed her directly in the face and continued to spray her "sort of methodically" over her head and parts of her body as the bags draped off her arms, Browne said. She turned and retreated to the back of the elevator.
Then, Browne said, the suspect pulled out a barbecue-style lighter, used it to ignite a rag in a bottle and then waited for a few seconds before using the flames to set her afire, causing smoke to fill the elevator.
The man backed out as she fell to the floor of the elevator, Browne said, and seemed to pause before tossing the bottle inside the elevator and onto her.
Browne wouldn't comment on the motive in the killing, but said the suspect knew Gillespie.
Police released still images of the man Saturday night, showing him in a black jacket, wearing what appear to be surgical gloves and with a white dust mask perched atop his head like a pair of sunglasses. He is holding what appears to be a canister with a nozzle and spraying as he steps into the elevator.
Neighbors reported a fire in the building, unaware that the woman was burning to death in the elevator.
Residents were evacuated and kept away from the six-story building for hours Saturday night as police investigated.