Arlington, Virginia - A shocking explosion that leveled a duplex in Arlington, Virginia, in December has been revealed to be an intentional act by a resident who was found dead inside, according to investigators. James Yoo, the resident in question, intentionally caused the blast using up to 35 gallons of gasoline, local and federal officials announced in a news conference on Friday.

The blast, which occurred on December 4, 2023, rocked a Northern Virginia neighborhood and completely destroyed the home of a neighboring family. Investigators determined that Yoo triggered the explosion in the basement using gasoline stored in three containers, one of which had a capacity of up to 20 gallons. It is believed that he ignited the gasoline using a gun, flare gun, matches, or a lighter, according to a U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) official.

"After a thorough and comprehensive investigation, our investigators determined that the incident was an intentional act by the decedent," stated Loannis Douroupis, resident agent in charge of ATF's Washington Field Office. "The decedent applied gasoline in the basement of the residence and ignited the vapors," he continued.

Yoo, who had previously been presumed dead, was confirmed as the deceased found within the wreckage of the duplex. Officials reported that he died from blunt force trauma and burns resulting from the explosion.

Police released officer body camera and dash cam video footage for the first time, providing new perspectives on the tragic event. The footage shows Yoo firing flares from an upstairs window of his home multiple times on the afternoon and evening of December 4. Throughout the incident, police repeatedly urged him to stop, and eventually warned that they would enter his home. Yoo responded by shooting gunfire from the house. Meanwhile, the natural gas supply to the duplex was turned off during the standoff.

Ultimately, police used an armored vehicle to breach the front door, and more gunshots could be heard coming from inside. Moments later, the explosion occurred. The blast was captured on video, showing orange flames shooting into the air while the roof collapsed, the walls bulged out, and debris flew in all directions.

Items found within Yoo's home following the explosion included at least three guns, two flare guns, ammunition, and flares. However, the FBI concluded that there was no connection to terrorism or any ongoing threat.

According to Arlington Police Chief Andy Penn, there were no documented prior incidents involving Yoo, except for two minor "noise-type complaints." Yoo had previously contacted the FBI with claims of fraud committed against him, although these tips did not result in any investigations.

Publicly, Yoo expressed grievances against several individuals in his life. His LinkedIn account contained paranoid rants about his neighbors and a former coworker. Yoo also filed multiple federal lawsuits against his ex-wife, younger sister, a moving company, and the New York Supreme Court, which were all dismissed as frivolous.

Neighbors reported witnessing strange behavior from Yoo, including large deliveries of lighter fluid, charcoal, and bleach to his home. He frequently covered his windows with black trash bags and rarely ventured outside.

Residents of the area have expressed mixed emotions upon learning the new details from investigators. Some find it unsettling, while others appreciate a sense of closure. The family who resided in the other half of the duplex declined to comment through their lawyers.

Regarding Yoo's motive, Chief of Police Andy Penn conceded that some questions may remain unanswered, saying, "As far as motive, unfortunately, we're not gonna know."

Stay informed as NBC Washington continues to provide updates on this developing story.