(ABC 6 News) — On Saturday, Donald Trump was shot at a rally in Butler, Pennsylvania, in what is being considered an assassination attempt.

The investigation into the attempt on the former president is ongoing, and new details have emerged regarding the shooter.

According to the FBI, on the day of the Trump rally, 20-year-old Thomas Crooks bought 50 rounds of ammunition from a gun shop. Later, Crooks obtained his father’s rifle after claiming he was going to a gun range.

Saturday’s assassination attempt has been in the spotlight as some wonder how shots were even fired in the first place.

“The buck stops with me,” said Director of the Secret Service Kimberly Cheatle in an ABC News interview. “I am the Director of the Secret Service, and I need to make sure that we are performing a review, and that we are giving resources to our personnel as necessary.”

Cheatle is set to testify before the House Oversight Committee on Monday.