Federal prosecutors have revealed that Cole Tomas Allen began planning his attack on the White House Correspondents' Dinner at least three weeks before the April 25 assault, according to a memo filed in federal court. Around 2 p.m. on April 6, the suspect searched "white house correspondents dinner 2026" on his cellphone and received a confirmation email from the Washington Hilton 90 minutes later for a room booked from April 24 to 26. prosecutors argued Allen poses "an uncommonly serious danger" and should remain detained pending trial on multiple charges including attempted assassination of the president.

The prosecution memo detailed how Allen, a tutor from California with an engineering and technology background, traveled across the country "armed to the teeth" to carry out an act of "unfathomable malice." He purchased a 12-gauge pump action shotgun in August 2025 and a .38 caliber pistol in October 2023, along with extra magazines, cartridges, two knives and four daggers. On April 21, he boarded a one-way Amtrak train from Los Angeles to Washington, bringing all his weapons. Law enforcement later found a respirator, duct tape and grip tape in his hotel room.

Allen arrived in Washington on April 24 and checked into the Washington Hilton at 3:15 p.m. He had pre-written emails to family, friends and his employer, scheduled to send shortly before the attack, each attached with a text file labeled "Apology and Explanations." At around 8:30 p.m., the emails were sent and Allen "rushed the screening checkpoint on the terrace level" of the hotel with a raised shotgun before being subdued by Secret Service officers.