The shot that killed the man who attempted to assassinate former President Trump at a rally in Butler, Pennsylvania, last Saturday was a "one-in-a-million shot," according to a source familiar with the investigation into the shooting.

Fox News learned from the source the kill shot was a single shot taken by a Secret Service counter sniper whose view was obscured.

A local tactical team also took a shot at the would-be assassin, 20-year-old Thomas Matthew Crooks, but missed.

The Secret Service sniper who killed Crooks could only see Crooks’ gun scope and the top of his eye and forehead because the lip of the roof was blocking the sniper’s view.

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Police snipers return fire after shots were fired while Republican presidential candidate former President Donald Trump was speaking at a campaign event

A sniper who shot Thomas Matthew Cooks, who attempted to assassinate former President Trump July 13, 2024, killed him with a single bullet with a "one-in-a-million shot." The snipers photographed did not take the fatal shot. (AP Photo/Gene J. Puskar)

The source described the shot to Fox News as a "one-in-a-million shot."

The news comes as more information begins to come out about the botched security detail that allowed Crooks to climb onto a building, get a clear line of sight of Trump and open fire on the former president.

While the Secret Service agents who stopped the shooter and jumped to protect Trump are being praised, the agency’s director, Kimberly Cheatle, has been harshly criticized for her handling of the matter.

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United States Secret Service Director Kimberly

Secret Service Director Kimberly Cheatle has been criticized and will face difficult questions about the security breakdown at the rally. (Kamil Krzaczynski /AFP via Getty Images)

The House Committee On Oversight and Accountability has scheduled a hearing for Monday with Cheatle, who is facing calls to resign from lawmakers over her agency's handling of the Trump rally shooting.

The hearing, "Oversight of the U.S. Secret Service and the Attempted Assassination of President Donald J. Trump," is scheduled to begin on Capitol Hill at 10 a.m. Monday.

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Donald Trump reacts as multiple shots rang out during a campaign rally

Former President Trump, a Republican presidential candidate, reacts as multiple shots rang out during a campaign rally at the Butler Farm Show in Butler, Pa., July 13, 2024. (Reuters/Brendan McDermid)

Cheatle is refusing to resign, but House Speaker Mike Johnson told FOX Business Thursday he is prepared to call on President Biden to fire her.

"Continuity of operations is paramount during a critical incident, and U.S. Secret Service Director Kimberly Cheatle has no intentions to step down. She deeply respects members of Congress and is fiercely committed to transparency in leading the Secret Service through the internal investigation and strengthening the agency through lessons learned in these important internal and external reviews," Secret Service spokesman Anthony Guglielmi said in a statement late Wednesday. 

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Cheatle was confronted by senators demanding answers when she showed up at the Republican National Convention in Milwaukee this week.

Fox News Digital's Greg Norman contributed to this report.