A massive explosion that destroyed an Arlington, Virginia, duplex in December was intentionally caused by the homeowner who died in the incident, fire officials said Friday.

The Bureau of Alcohol, Tobacco, Firearms and Explosives and the Federal Bureau of Investigation joined Arlington County Police and Arlington County Fire to investigate the explosion.

Investigators detailed the incident in their report, beginning with the first officer's arrival on the scene, according to Fox 5 DC. Body-worn camera video was also released showing new angles of the explosion and of homeowner and suspect James Yoo, 56, firing flares from his window.

The explosion started in the basement of the home and involved gasoline and a "competent ignition source," according to officials. They said "munitions used by police during this incident are verified not to be a competent ignition source."

VIRGINIA HOME EXPLODES AFTER BARRICADED SUSPECT FIRES FLARE GUN, FIREARM WHILE POLICE ATTEMPT SEARCH

A massive explosion that destroyed an Arlington, Virginia, duplex in December was intentionally caused by the homeowner who died in the incident, fire officials said Friday. (Credit: Alex Wilson)

Items found at the scene included gasoline canisters, two shotguns, two flare guns, shotgun magazines, loose shotgun rounds and fired and unfired flares.

Yoo's death was ruled to have been caused by "thermal injuries and blunt force trauma," according to officials.

Neighbors said Yoo had been acting erratically in the months leading up to the incident. He allegedly ordered large quantities of bleach and charcoal before the explosion and covered his windows with black trash bags. The morning of the incident, he threw garbage onto his lawn, including empty bleach bottles.

Later that day, he began firing flares out of the back window of his duplex. Police investigated the scene and unsuccessfully attempted to make contact with Yoo.

WHO IS JAMES YOO, MAN LINKED TO ARLINGTON HOUSE EXPLOSION IN VIRGINIA

The explosion started in the basement of the home and involved gasoline and a "competent ignition source," officials said. (Credit: Alex Wilson)

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Police obtained a search warrant and forced their way through his front door with an armored vehicle. As officers reached the door of his home, Yoo fired multiple gunshots from within the house, officials said.

Officials said they turned off gas service to the home and evacuated nearby residents about an hour and a half before the explosion.