Allen is accused of carrying a semi-automatic handgun, a pump-action shotgun and three knives as he charged past a security checkpoint at the White House Correspondents’ Association dinner on Saturday.
During Saturday night’s incident, Trump, Vice-President JD Vance, cabinet members, and other White House officials were rushed from the Washington Hilton hotel ballroom after gunfire rang out.
A Secret Service agent was shot but not seriously wounded during the attack at the hotel. Allen faces life in prison if found guilty.
In the new memorandum, prosecutors say Allen took photos of himself in his hotel room with his cell phone at around 20:03 EST (1:03 BST) wearing dress clothes as well as a shoulder holster, pliers and wire cutters that they say were later recovered from Allen.
The government alleges that for the next half hour, Allen checked several websites for live coverage of the White House Correspondents’ dinner, and for the president’s attendance. He then made his way downstairs and towards the ballroom, where the dinner was taking place.
Prosecutors allege Allen discarded a long black coat that had concealed a pump-action shotgun.
“Shortly thereafter, the defendant rushed the screening checkpoint on the Terrace Level of the Washington Hilton with a raised shotgun,” the memo states.
He sprinted through a metal detector, holding the shotgun with both hands in a raised position, the government says.
