This June 3, 2022 still image taken from video provided by the Bethel Park School District shows student Thomas Matthew Crooks in the 2022 Bethel Park High School Commencement in Bethel Park, Pa. (The Bethel Park School District via AP)

The gunman who attempted to assassinate Donald Trump purchased 50 rounds of ammunition at Allegheny Arms and Gun Works in Bethel Park hours before the former president's rally in Butler on Saturday, the Post-Gazette has learned.

In a message to the PG, a spokesperson for Allegheny Arms wrote: "As a responsible member of our community it is our prerogative to cooperate with law enforcement in every way. We are thankful that President Trump was not assassinated, and our hearts and prayers go out to all victims of this horrible incident. Out of respect for the ongoing investigation and that of those affected we will not make any further statements."

This 2021 photo provided by Bethel Park School District shows student Thomas Matthew Crooks who graduated from Bethel Park High School with the Class of 2022, in Bethel Park, Pa. Crooks was identified by the FBI as the shooter involved in an assassination attempt of former President Donald Trump at a campaign rally on Saturday, July 13, 2024, in Butler, Pa. Bethel Park School District via AP

The gun store is complying with all requests from law enforcement, sources said. Store officials declined to release more information on the ammo purchase.

Officials say Thomas Matthew Crooks, 20, took his shots with an AR-style 5.56-caliber rifle from the roof of a building about 150 yards from where Trump was speaking, killing 50-year-old Corey Comperatore, injuring David Dutch, 57, and James Copenhaver, 74, and leaving the former president bloodied and ducking for cover.

Sources told CNN the Secret Service did not sweep that building but instead left that to local law enforcement. CNN also reported Crooks was scheduled to work his shift at a nursing home Saturday but requested the day off because he “had something to do.”

According to the FBI, investigators also found "rudimentary" explosive devices and bomb-making material inside Crooks' car and in the home he shared with his parents in Bethel Park.

A spokeswoman for the Bureau of Alcohol, Tobacco, Firearms and Explosives said investigators were able to quickly trace the gun Crooks used.

"ATF was on the scene within minutes and completed an urgent trace through ATF's National Tracing Center based on out of business records from a closed gun dealer," spokeswoman Kristina Mastropasqua said in a statement.

She said bureau investigators traced the gun within 30 minutes, helping the FBI and Secret Service to identify Crooks.

Mastropasqua said the bureau also was helping to investigate the explosive devices and apparent bomb-making material.

Federal authorities say they're investigating Saturday's shooting not just as an attempted assassination, but a possible act of domestic terrorism.