Washington DC - Recent court documents filed by the Department of Justice reveal new details about the days leading up to suspected gunman Cole Allen's attack at the White House Correspondents' Dinner.

On Wednesday, US Attorney Jeanine Pirro filed a memorandum in support of pretrial detention, which argued Allen's alleged actions were "premeditated, violent, and calculated to cause death" and "an anti-democratic act of political violence."

The filing claims that on April 6, a month after President Donald Trump revealed he would be attending the dinner, Allen began using his cell phone to search the internet about the event.

That same day, he booked a room at the Washington Hilton – where the event was scheduled to be held on April 25 – for April 24-26.

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On April 21, Cole took a long train ride from his home in California to Washington DC, during which he "kept a running note on his phone of his observations and thoughts" and continued to thoroughly research the gala.

On Saturday at 8:03 PM ET, moments after the event officially kicked off, Allen took a selfie from his room.

The image, featured in the memo, appears to show the 31-year-old suspect with several items strapped to himself, including a sheathed knife, a gun holster, pliers, and wire cutters.

Around 8:30, he prescheduled emails to his family containing his reported manifesto, which he titled "Apology and Explanation." Moments later, he rushed through security, exchanging fire with law enforcement until he was arrested.

The memo provides new information about the lead-up to the attack, but questions still remain about what exactly took place after Allen managed to get through security.

So far, surveillance footage shared by Trump on his social media page does not capture the full exchange of gunfire.

While law enforcement sources told CBS News that a final ballistics analysis is still pending, they did confirm that one officer fired five rounds, none of which hit Allen.

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The memo claims Allen fired a single round from a 12-gauge shotgun "in the direction of the stairs leading down to the ballroom."

Though he wasn't on the same floor as his intended targets, Allen has been charged with attempting to assassinate Trump, which could land him in prison for life.