Alleged Gunman in 'Pizzagate' Case Pleads Not Guilty to All Charges

— -- Alleged "pizzagate" gunman Edgar M. Welch pleaded not guilty this morning to all charges stemming from the incident.

Welch is charged with a federal offense of interstate transportation of a firearm and ammunition, a District of Columbia offense of assault with a dangerous weapon, and a D.C. offense of possession of a firearm during the commission of a crime of violence.

He was arrested earlier this month after allegedly walking into a Washington pizza place with a loaded AR-15 rifle and firing shots to "investigate" the false rumors that the restaurant was harboring children.

The establishment got swept up in a flurry of fake news reports and social media postings that linked the restaurant to Hillary Clinton and a trafficking ring.

Michael Flynn Jr. -- the son of Trump's national security adviser pick, retired Lt. Gen. Michael Flynn -- was forced out of the Trump transition team amid the fake news controversy after he pushed the "pizzagate" conspiracy theory in a flood of tweets.

On Sunday, Dec. 4, Welch got in his car and drove from his hometown in North Carolina directly to the pizzeria.

In a text message to his girlfriend a few days before, Welch wrote that he had been researching the "pizzagate" conspiracy theory and it was making him "sick," according to the criminal complaint against him.

Around 3 p.m., he arrived at the restaurant, where witnesses say they saw Welch holding the rifle across his chest, according to the complaint. He was carrying a loaded assault rifle and a fully loaded .38 caliber Colt revolver, according to court documents filed by the prosecution.

At that point, patrons and staff fled the building.

While inside, he encountered a locked door and attempted to open it with a butter knife, the complaint says. When that didn't work, he fired shots at the lock with his AR-15, documents say. Still unsuccessful at opening the door, he climbed on top of furniture to look inside the locked room and found it empty, according to the complaint.

Less than a half hour later, Welch exited the building with his hands in the air and complied with officers’ instructions.

Welch was first charged in D.C. court, but now faces federal charges as well. He has been detained since his arrest.

He was arraigned in federal court and scheduled for a detention hearing this morning. However, his attorney conceded that he would remain in detention.

"He understands the nature of the charges in the indictment," said Assistant Public Defender Dani Jahn of her client after the hearing, declining to comment further.

The U.S. Attorney’s office also declined to comment outside of the courtroom. Welch is scheduled for a status hearing on Jan. 5, 2017.

ABC News' Ali Dukakis and Katherine Faulders contributed to this report.