Prosecutors announced Wednesday that Jerome Isaac had pleaded guilty to first-degree murder, arson and torture in the December 2011 death of Deloris Gillespie in Brooklyn.
The plea bargain calls a sentence of 50 years in prison.
Prosecutors say Isaac attacked the 73-year-old woman because he believed she owed him money. They say he doused her with gasoline, lit her on fire and then threw a firebomb inside the elevator.
The attack was recorded on a security camera.
Isaac is scheduled to be sentenced on Nov. 30.