New York City police say a man charged with setting a woman on fire in an elevator was angry because she owed him $2,000 US.

Authorities say Jerome Isaac told them he set 73-year-old Deloris Gillespie ablaze because she owed him money for work he had done. Isaac, 47, faces murder and arson charges in her death.

Police say Isaac reeked of gasoline when he walked into a police station overnight and admitted his role in Gillespie's death.

They say Isaac ambushed Gillespie in the elevator of her Brooklyn apartment building on Saturday afternoon, doused her with an accelerant and then set her afire with a Molotov cocktail. 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,” Browne 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, police said.

Sprayed victim 'methodically' with liquid

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, according to Browne.

She turned and retreated to the back of the elevator. Then, 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 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.

Neighbours 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.

Man may have lived with Gillespie

Jaime Holguin, who lives on the same floor as Gillespie, said he and his girlfriend had taken the elevator on their way out of the building shortly before the attack.

He said the man in the photos released by police looked like a man who had lived with Gillespie for about six months or so toward the end of 2010.

"It seemed like during the time he was here, he was kind of helping her out in her apartment," Holguin said.

The man seemed to stop staying there around the beginning of 2011, but Holguin said he spotted him on the street near the building months after that.

"When we started to see him on the street, he looked a lot more dishevelled," Holguin said.