New images included in a memorandum filed by the US government show Cole Tomas Allen - the man accused of opening fire at a White House Correspondents' dinner last weekend - with weapons in a hotel room before the attack.
Prosecutors submitted the photos along with new details of the suspect's activities before the 25 April incident in their motion to keep Allen detained pending trial.
The 31-year-old has pleaded not guilty to several charges, including attempting to assassinate President Donald Trump.
Prosecutors say the photos show Allen in his hotel room posing in front of a mirror with several weapons strapped to his body, including a sheathed knife, and a bag with ammunition.
Department of Justice
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.
The new filing also alleges that Allen kept a note on his phone of observations of his surroundings as he traveled from his home in California across the country to Washington, including "[t]he southwest desert in spring Distant wind turbines looming like snowy mountains across the hazy NM desert".
Prosecutors argue in the filing that Allen should remain detained before his trial, calling his alleged actions "premeditated, violent, and calculated to cause death".
"Considering the relevant statutory factors, there is no condition or combination of conditions that will reasonably assure the safety of other people or the community if the defendant were released from custody," prosecutors say.
The other charges Allen faces - transportation of a firearm between states to commit a felony and discharging a firearm in a crime of violence - both have maximum sentences of 10 years.
Officials have said the suspect left his home in the city of Torrance in the Los Angeles area on 21 April, travelling by train to Chicago before heading to Washington.
According to an affidavit, the accused sent an email to his family shortly before the attack that said, "Administration officials... are targets, prioritized from highest-ranking to lowest".
"I would still go through most everyone here to get to the targets if it were absolutely necessary," he allegedly added.
