Terror was caught on tape as firemen walked into a killer's ambush.
Radio communications were recorded from one of the firemen who responded to the blazing homes, only to find they had been lured there by a murderer armed to the teeth and thirsting for blood.
A firefighter said on the recordings, "We are being shot at. Multiple firemen down. Multiple firemen shot. I am shot. I think he's using an assault rifle."
A dispatcher tried to warn other first responders who were on the way.
Dispatcher: "Multiple shots being fired at the location. You are to stage away from the area until cleared."
The shooter was William Spengler, who once did 17 years in prison for murdering his grandmother with a hammer. This time, he torched his own house, then lay in wait with a stash of guns.
Two firemen were killed in the horrific ambush. Thomas Kaczowka who was just 19, and Michael Chiapperini who had been named Fireman Of the Year just a few days before.
Spengler killed himself as a SWAT team closed in. He left a horrific note.
Police Chief Gerald Pickering said, "He was going to go burn as many houses as possible and do what he really liked to do, and that was kill people."
Authorities also found a body believed to be the shooter's sister in the smoldering wreckage of the house.
Spengler had opened fire with the same weapon used in the Newtown School massacre, the controversial Bushmaster rifle.
Security expert Steve Kardian, who demonstrated the weapon's fearsome firepower for INSIDE EDITION, says an ambush like the one in Rochester, New York, is a first responder's worst nightmare.
"Firefighters and EMS are showing up with the intent to put out the fire and tend to the injured. They're not showing up with the intent that they're going to be fired upon. That's the last thing on their minds...until today.