New York ( CNN ) -- A man who ambushed firefighters Monday , fatally shooting two of them as they arrived to put out a raging inferno in upstate New York , took his own life with gunshot to the head , according to an autopsy conducted by the Monroe County Medical Examiner 's Office . Two other volunteer firefighters were wounded in the attack in the Rochester-area town of Webster . Authorities do not know how William Spengler , 62 , who was found dead hours after the four firefighters were shot , obtained the weapon or weapons he used or why he opened fire . Shooter who ambushed firefighters left note showing intent to burn , kill . As a convicted felon , Spengler could not legally possess guns , but he had `` several different types of weapons , '' Webster Police Chief Gerald Pickering said . Spengler was convicted in 1981 of first-degree manslaughter in the death of his grandmother and had been released on supervised parole . `` It appears that it was a trap , '' Pickering said . `` There was a car and a house that were involved in flames , probably set by Mr. Spengler , who laid in wait in armament and then shot the first responders . '' In audio heard over a scanner , a West Webster Fire Department firefighter reported `` multiple firemen shot '' -- including himself , with wounds to his lower back and lower leg -- and `` shots still being fired . '' 'Brother , hang tight , ' wounded New York firefighter told as two colleagues lay dead .
Autopsy shows that William Spengler took his own life with a gunshot to the head . He killed two firefighters as they arrived to put out a raging inferno in upstate New York . Authorities say they do n't know how Spengler , 62 , obtained the weapon or weapons he used .