The man who ambushed and killed two firefighters in Webster, New York on Monday left a note saying he wanted to "burn down his neighborhood and kill as many people as possible," police said on Tuesday.

Webster Police Chief Gerald Pickering also said the gunman, 62-year-old William Spengler, was armed with a 12-gauge pump shotgun, a .38-caliber revolver and an AR-15 .223 caliber rifle during his attack, in which Spengler allegedly set his own house on fire, then took cover before launching his assault. The rifle is the same kind of assault weapon used in the Dec. 14 school shooting in Newtown, Connecticut.

"This was a clear ambush on first responders," Pickering said, adding that his department is still investigating how Spengler acquired the firearms.

Spengler was found dead at the scene from a self-inflicted gunshot wound. A handwritten note was also found nearby, though not at his house. Pickering said it did not mention a specific motive, but was clear on his intent.

"I still have to get ready to see how much of the neighborhood I can burn down and do what I like doing best: killing people," Spengler wrote, according to Pickering.

Two other firefighters and an off-duty police officer were also injured in the attack, Pickering said, and seven homes were destroyed in the fire. Two more were left uninhabitable.

UPDATE, 4:23 p.m. EST: The Associated Press reported that authorities found a burned body in the wreckage of Spengler's home, and believe it to be his sister, Cheryl, who lived with him.

Watch this report from CBS News, aired Tuesday, below.