A New York man, who shot dead two firefighters and injured as many, had spent 18 years in prison for beating his grandmother to death with a hammer.

William Spengler, 62, burnt down a house and car in Webster on Monday and as firefighters reached the scene to put out the blaze, Spengler shot at them.

Webster Police chief Gerald Pickering told reporters that police lieutenant Michael Chiapperini, 43, and Tomasz Kaczowka, 19, a 911 dispatcher for Monroe were killed by Spengler, who was armed with rifles.

Pickering said police had exchanged fire with Spengler, who later died of a self-inflicted gun shot wound to the head.