The suspect in the White House Correspondents' Dinner shooting appears to have started planning the attack three weeks ago when he began to search online about the event, according to new details in a memorandum prosecutors filed Wednesday in federal court. 

The filing includes more information about suspect Cole Allen's alleged movements on Saturday night, his apparent state of mind during his cross-country train trip to Washington, D.C., and how he allegedly planned the attack. It also includes a photo prosecutors say Allen took of himself in front of a mirror in his hotel room just before the attack, showing multiple weapons. 

"The defendant's actions were premeditated, violent, and calculated to cause death," prosecutors wrote in the memorandum. "It was, at its core, an anti-democratic act of political violence." 

Allen has been charged with multiple counts including attempting to assassinate the president of the United States. Allen's lawyers have not responded to requests for comment from CBS News.

The timeline laid out by prosecutors notes that on March 2, President Trump publicly announced that he would attend the White House Correspondents' Dinner in a post on his Truth Social account. It was the first time he'd agreed to attend as president.

On the afternoon of April 6, prosecutors say Allen, who was then in his home state of California, used his cellphone to search "white house correspondents dinner 2026" and visited the page about the dinner on the White House Correspondents' Association website.  

On the same day, they say,  Allen booked a room at the Washington Hilton, the venue for the April 25 dinner, for April 24-26.   

Then on April 16, prosecutors say, he again used his phone to access articles discussing the dinner, including its host, CBS News senior White House correspondent Weijia Jiang, and the event schedule and expected attendees. 

Allen purchased a one-way Amtrak train ticket from Los Angeles to Washington, D.C., via Chicago, prosecutors say. And on April 21, he booked a car with a ride share app to travel from his home in the suburb of Torrance to Los Angeles Union Station to board the train. 

During his trip across the country, Allen "kept a running note on his phone of his observations and thoughts," prosecutors say. 

His notes, according to prosecutors, included, "[t]he southwest desert in spring Distant wind turbines looming like snowy mountains across the hazy NM desert," "Chicago is cool; kinda like an Iowa small town was scaled up to LA size," and Pennsylvania's "woods are awesome (look like vast fairy lands filled with tiny trickling creeks in spring apparently." 

Prosecutors say he also used the train ride  to research the White House Correspondents' Dinner and the president's plans, viewing an article titled "Trump's Plans for 'Mic-Drop' Media Confrontation Are Leaked: The president is planning a rage-fueled moment at the White House Correspondents' Association dinner." 

Prosecutors say Allen changed trains in Chicago on April 23 and on the next leg continued reading articles related to the event, including a piece titled "Social Scene: Your Guide to the 2026 White House Correspondents Dinner Weekend." 

When he got to D.C. on Friday, April 24, at 1:10 p.m., prosecutors say, he took the Metro train to the Washington Hilton and checked in around 3:15 p.m.

On Saturday, the day of the event, Allen came and went from his room multiple times, and looked up the president's schedule using a "civic tracker" website at around 6:26 p.m., according to prosecutors.

Then at 8:03 p.m., just three minutes after the official start of the event, he stood dressed in a black dress shirt, a bright red tie tucked into his pants, and armed with weapons, to take a photo of himself in the mirror, the hotel bed visible behind him. A plastic bag is seen on the hotel room desk in the foreground. The photo is included in the prosecutors' memo.

A digitally enhanced close-up version of the photo included in the memorandum, with annotations by the Justice Department, shows Allen wearing a small leather bag, a shoulder holster, a sheathed knife, pliers and wire cutters, according to prosecutors. The memo says they  appear to match items recovered later by law enforcement.

Ten minutes after taking the photo, Allen rechecked the "Presidential Schedule – CivicTracker" webpage before leaving his hotel room a couple of minutes later, prosecutors say.

According to the DOJ timeline, he was on his phone searching live videos of the dinner until just before he rushed the magnetometers.

At about 8:27 p.m., he accessed the video "WATCH LIVE: President Trump, first lady en route to White House Correspondents' Dinner," and watched Mr. Trump exiting his vehicle to attend the dinner in another video, the memorandum says.

At about 8:30 p.m., Allen's prescheduled emails, containing a text file titled "Apology and Explanation," were sent to members of his family. The message stated that he planned to target Trump administration officials, "prioritized from highest-ranking to lowest," according to a copy obtained by CBS News. 

And right after that, prosecutors say, he rushed the screening checkpoint on the terrace level of the Washington Hilton with a raised shotgun.

A U.S. Secret Service officer "observed the defendant fire the shotgun in the direction of the stairs leading down to the ballroom," the memo states.

The memorandum supplies the most detailed account of his movements leading up to the event, but questions remain about what happened when he appeared to run past security and shots were fired. Law enforcement sources told CBS News the final ballistics analysis is pending.

One law enforcement officer fired five rounds, some of the bullets hitting the hotel walls, none of them hitting Allen, law enforcement sources told CBS News. Surveillance video shows an officer in black clothing and a vest with "Police" on it raising his firearm and aiming at Allen.  

It remains unclear if the bullet from Allen's shotgun was recovered from the scene. Acting Attorney General Todd Blanche told reporters Monday that the shell casing from that shot stayed inside the shotgun.

Prosecutors are seeking pretrial detention and have charged Allen with attempted assassination of the president, which carries a maximum sentence of life imprisonment. Allen is also charged with discharging a firearm during a crime of violence and transporting firearms across state lines intending to commit a felony.

"Had the defendant achieved his intended outcome, he would have brought about one of the darkest days in American history," prosecutors wrote in the memorandum. "The defendant traveled across the country with the explicit aim to kill the President of the United States."

They allege that Allen, armed with a 12-gauge shotgun, a .38 caliber pistol, two knives, four daggers and enough ammunition to take dozens of lives, was apprehended by Secret Service officers "mere feet away from the ballroom where his primary target was located, along with other members of the Cabinet."