Police say those materials include an anti-tank rocket used for training by the military and some highly explosive chemicals.
The scene unfolded at 71 Barry Road in New Britain Township.
At nine o'clock Tuesday morning, police and paramedics responded to a call of a man in cardiac arrest. They found the homeowner, 34-year-old Christopher Kanter, a software engineer, unresponsive in the kitchen. He'd been dead for hours.
Police then discovered an inert anti-tank rocket in a container in the living room.
In the basement, kitchen and bedroom they found large quantities of a black powder, fireworks, and liquid chemicals including pitric acid, which is highly explosive in its crystallized form.
"It looked like he was making improvised explosive devices," said New Britain Twp. Police Chief Robert Scafidi. Scafidi added that authorities have no idea if he had any intention of using them.
ATF agents and other explosives experts closed down the street and set up a mobile lab to analyze the dangerous chemicals stockpiled inside the home.
"There's a chemist here checking what they are," said Scafidi, "what can be removed and what has to be detonated on the scene."
Police had not been called to the home before for anything unusual, just medical calls. Kanter lived here with his girlfriend and had a house guest from North Carolina.
Neighbors said they only saw him coming and going. But they heard him firing weapons and setting off fireworks sometimes in the middle of the night.
They never imagined he'd acquired enough explosive materials to do some serious damage.
"It's just unnerving," said neighbor Jessica Kosluk. "There are children and families. Just to live right next door, could have killed any one of us. Anyone."
The bomb squad, hazmat and ATF expect to be on the scene into Tuesday evening. Some of the chemicals are too dangerous to even transport, so they will be detonated here.
Police do not think Kanter's girlfriend or the house guest had anything to do with what they found. An autopsy will be performed to determined how Kanter died.