Police said they found an arsenal of explosives, firearms and ammunition in a home in Fairfield, Conn., last night after conducting a welfare check on Bronson Road.
Police said they went to the house on Tuesday morning when someone from out-of-state called to ask that they check on the man who lived there.
A source close to the investigation identified the homeowner as Joseph Callahan.
Callahan, who lives alone, later called police himself and said he thought there was a burglary at the house, police said.
When officers went back to investigate, Callahan appeared to be "out of sorts," and police said they saw a "significant" amount of chemicals that caused concern.
Several agencies, including state police, the FBI and Alcohol, Tobacco, Firearms and Explosives Task Force, were brought in to help with the investigation.
When crews determined that it was safe to enter the house, they also found hundreds of firearms, thousands of rounds of ammunition, chemicals and explosives, along with 250 galls of jet fuel, according to police.
Police said the chemicals found in Callahan's home are not dangerous, but could become dangerous if combined.
Callahan, who is in his 60s, was taken to the hospital for an evaluation, police said.
Police said it appears Callahan has a background in chemistry and a hobby involving rockets.
Some of the items found in the house are legal, police said, but others seem to be illegally manufactured explosive devices.
"We don't know the reasons why he did this," said Fairfield police Lt. James Perez. "We don't know who he's connected to, but I will tell you we are doing a thorough investigation now."
Police said they've obtained an arrest warrant for Callahan and that he will be arrested when he gets out of the hospital.
During the investigation, police diverted traffic and evacuated neighbors as a precaution.
"Even if he didn't have any ill intent, to have chemicals firearms and explosives, that's a puzzle for disaster, and we're thankful nothing happened," said Fairfield police Chief Gary MacNamara.