New details tonight in a deadly home explosion in Arlington, Virginia. Authorities now releasing dash cam video of the moment the house exploded during a standoff between the homeowner and law enforcement. And tonight, what investigators say caused the massive blast? Here's ABC's Perry Russa.

It was the dramatic home explosion that rocked a neighborhood miles outside Washington, DC. Tonight, new video showing the Heart stopping moments. This police officer running for cover as debris rockets toward him. Investigators now saying the blast from December was intentionally said. Mr.

You.

Officers confronting James You in an hour's long standoff, You barricading himself inside after firing dozens of flares from a window. Police breaching the front door. Seconds later, gunshots heard from inside. Ten minutes later, that explosion. Police say You, who posted hundreds of pages of conspiracy theories online, exploded his own house using 35 gallons of gasoline.

And, Whit, police say they found two shotgun, a handgun, and two flare guns in the rubble of the house. Investigators say they believe he lit the gas on fire in his basement.

Whit? Perry Russam for us tonight. Thank you.