Story highlights As shots rang out, a wounded firefighter reported "2 DOAs" on the street

Investigators believe the gunman set a trap for the firefighters who responded

William Spengler, who killed his grandmother decades ago, was found dead

Seven houses were destroyed in what police described as an "inferno"

A man convicted of killing his grandmother decades ago ambushed firefighters on Monday, fatally shooting two of them as they arrived to battle a blaze in upstate New York, police said.

Two other volunteer firefighters were wounded in the attack in the Rochester-area town of Webster. A police officer from the nearby town of Greece suffered minor shrapnel wounds when his vehicle was hit by gunfire.

Investigators believe the suspect, William Spengler, 62, set the original fire, then likely set himself up on a berm with a clear view of the scene and started shooting.

"It appears that it was a trap," Webster Police Chief Gerald 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."

Investigators say that William Spengler, 62, deliberately lured firefighters to the house fire.

Authorities do not know how Spengler -- who was found dead of a self-inflicted gunshot wound hours after the four firefighters were shot -- obtained the weapon or weapons he used or why he opened fire, Pickering told reporters. As a convicted felon, Spengler was not allowed to legally possess weapons, but he had "several different types of weapons" Monday, the police chief said.

Spengler was convicted in 1981 of first-degree manslaughter in the death of his grandmother and had been released on supervised parole, Pickering said.

He is believed to have lived in the home where the original fire erupted with his sister, who has not yet been accounted for, Pickering said. Their mother died sometime in the past year, the chief added.

In chilling audio heard over the 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."

"I'm pretty sure that we have two DOAs" -- the term for dead on arrival -- "on the street," the wounded firefighter said. "... They're down and not good."

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For several hours after that Monday, the threat of gunfire stopped firefighters from battling the blaze and forced police SWAT teams to evacuate 33 people in the neighborhood of small, waterfront homes.

Eventually, seven houses were "totally destroyed" by the fire. Although the fires were under control as of 2:30 p.m. ET, by then authorities still hadn't been able to get in any of the homes. Pickering said it's possible more victims could be inside.

"I'm hoping that everyone was able to escape from the inferno," he said. "Those houses were close together."

With 'raging inferno' and gunfire, scene described as 'chaos'

Firefighters first arrived at the Webster fire before 6 a.m., said Rob Boutillier, the town's fire marshal.

By then, Spengler had set up himself somewhere above the scene in a "natural hollow, a position of cover to actually be a sniper," Pickering explained.

The calls from firefighter came in soon after, reporting that four of them had been shot. Police officers rushed to the scene, and one of the first ones there exchanged fire, "in all likelihood, (saving) many lives," according to the police chief.

"When we get there, we have people down, we have raging fires, and we have gunshots going off," Pickering said.

"It's chaos. It's chaos."

Authorities worked quickly to set up a perimeter, trying to contain the situation and the shooter. Neighborhood residents were first told to "shelter in place" because the gunman was at large, but some left their homes because of the fire.

Several people could be seen running. Police tracked some of them down, found they were neighbors seeking safety and escorted them out. Eventually, residents were whisked from the area in armored personnel carriers. All the while, there was "this raging inferno, with black smoke everywhere," Pickering said.

No more gunfire was exchanged after that initial burst, though police did see a man they believed to be Spengler moving at times. The police chief said he didn't know if the police officer hit Spengler early on, but he said the medical examiner indicated that Spengler died after shooting himself in the head.

Two firefighters also died at the scene.

One of them, Lt. Michael Chiapperini, was a veteran of the West Webster Fire Department and a police lieutenant. He'd been named Firefighter of the Year just two weeks ago, and not long before that, he had volunteered to go to Long Island to help those suffering after Superstorm Sandy, according to Lt. Gov. Bob Duffy.

Police have identified one of the firefighters killed as Lt. Mike Chiapperini.

The other slain firefighter was Tomasz Kaczowka, who was also a 911 dispatcher. He'd been with the West Webster Fire Department for just more than a year, fire department spokesman Al Sienkiewicz said.

One firefighter escaped from the scene in his own vehicle about an hour after he was shot and was taken to a hospital by an ambulance from another location, Boutillier said. Another wounded firefighter was conscious and speaking when he was removed from the scene, he said.

The wounded firefighters were in intensive care Monday at Strong Memorial Hospital in Rochester, New York, officials said.

The other person wounded was a Greece, New York, police officer who was on his way to work when his car was fired upon. He suffered shrapnel wounds that Pickering described as minor.

"We work with these people everyday; they're like our brothers," said Pickering of the slain firefighters, as he fought back tears. "It's terrible."

New shooting spurs more talk on gun control

Authorities have not said what weapons were found with Spengler, though Pickering said "probably at least a rifle was used" to shoot the first responders.

"I know that many people are going to be asking, 'Were they assault rifles?' I don't know that. I can't answer that at this time," he told reporters.

The shooting occurred amid a renewed gun control debate after the December 14 elementary school massacre in Newtown, Connecticut, that killed 26 people, most of them children. The gunman in that case, Adam Lanza, also killed his mother and himself.

The head of a lobbying group that represents first responders said the Monday shooting was "senseless and cruel."

"The firefighters who responded today were performing a selfless, meaningful service to their community, unaware that a cold-hearted maniac was planning to ambush them and take their lives," said Harold Schaitberger, general president of the Washington-based International Association of Fire Fighters. "Coming on the heels of the horrific tragedy in Newtown, Connecticut, and on Christmas Eve, this shooting is even harder to comprehend."

New York Gov. Andrew Cuomo described the Webster shooting as "horrific." And the state's attorney general called it a "senseless tragedy"

President Barack Obama has set a January deadline for "concrete proposals" to deal with gun violence in the wake of the Newtown school shooting.

Sen. Dianne Feinstein, D-California, has said she will introduce legislation to reinstate the assault weapons ban that expired in 2004, while National Rifle Association CEO Wayne LaPierre has said his group will fight any new gun restrictions , saying most gun laws now on the books are rarely enforced.

Pickering, the Webster police chief, said it was important -- in the wake of the shooting in his town and others -- to "get a handle on gun control." He also said more needs to be done to make sure that dangerous people aren't in society, where they can kill.

"For the last 20 years we have been turning people loose and deinstitutionalizing people, and I think we've swung too far," he said. "I think there are still people that need to be in institutions that are a danger to themselves or others. And this is a classic example."