The 20-year-old would-be assassin who fired at former President Trump in Pennsylvania over the weekend was found with a Home Depot receipt for a ladder, sources told NBC News.

Investigators discovered the item on Thomas Matthew Crooks after he was fatally shot by Secret Service agents on Saturday.

Officials are now trying to determine if Crooks used the ladder to access the roof of the building from which he blasted Trump in the ear, sources told the outlet.

Exterior view of The Home Depot where Donald Trump's would-be assassin purchased a ladder.

Exterior view of a Home Depot store in Bethel Park, Pennsylvania. (Sarah Rumpf / Fox News Digital)

Fox News Digital reached out to Home Depot, which referred questions to law enforcement.

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An undated image of Thomas Matthew Crooks.

File photo of Thomas Matthew Crooks.  (Handout via AFP)

More than a dozen firearms were discovered inside the Crooks family home, and the shooter's father called police to tell them his AR rifle was missing after the incident.

The rifle used in the shooting was purchased legally, and may have been his father's. 

Law enforcement agents are also investigating if the bullets were bought at Allegheny Arms and Gun Works in Bethel Park.

The store is a brief drive from the Crooks' family home.

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Donald Trump gestures with a bloodied face as multiple shots rang out during a campaign rally

Former U.S. President Donald Trump gestures with a bloodied face as multiple shots rang out during a campaign rally at the Butler Farm Show in Butler, Pennsylvania, U.S., July 13, 2024.  (Brendan McDermid/Reuters)

Several videos show rally goers alerting local law enforcement agents to Crooks' presence on top of the structure prior to the shooting.

Officials have said Crooks acted alone in trying to kill Trump but are still investigating.

Undated file photo of Thomas Matthew Crooks

Undated file photo of Thomas Matthew Crooks. Crooks is alleged to be the shooter in the assassination attempt on former President Donald Trump in Butler, Pennsylvania on Saturday, July 13, 2024. (Obtained by Fox News Digital)

Scant details have emerged about Crooks' background or motivation. Locals have said he was the victim of relentless bullying at his high school and a perpetual loner.

Classmates described him as a conservative, but noted that he wasn't vocal about his political views.

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Aerial view of the scene of the Trump rally where an assassination attempt was made on the former President

A drone view during the police investigation into gunfire at a campaign rally of Republican presidential candidate and former U.S. President Donald Trump in Butler, Pennsylvania, U.S. July 14, 2024. (Carlos Osorio/Reuters)

While he was a registered Republican, Crooks also appeared to donate $15 to the Progressive Turnout Project in 2021.

Crooks, who was a member of a shooting club, frequently wore hunting outfits to school and was mocked for them, according to reports.

Former Buffalo Township Volunteer Fire Company Chief Corey Comperatore, 50, was struck by one of Crooks' bullets and killed at the rally.

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Attendees James Copenhaver, 74, and David Dutch, 57, were both critically injured and remain in stable condition.

Trump was hit in the ear before ducking from the bullets.