The attempted assassination of former President Donald Trump during a campaign rally Saturday was “unacceptable,” according to the head of the U.S. Secret Service.

“It was unacceptable,” Kimberly Cheatle told ABC News in her first interview since the Saturday evening attack. “And it’s something that shouldn’t happen again.”

“The buck stops with me,” Cheatle added. “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.”

However, Cheatle said she would not resign.

The interview was Cheatle’s first in roughly 48 hours since the suspect, identified as 20-year-old Thomas Matthew Crooks, opened fire atop a roof outside the security perimeter at the event in Butler, Pennsylvania.

One rallygoer, Corey Comperatore, was killed and others were wounded in the attack.

Cheatle defended her agents from witness reports that the shooter had been spotted and reported to police on site before opening fire.

“I don’t have all the details yet, but it was a very short period of time,” Cheatle said. “Seeking that person out, finding them, identifying them, and eventually neutralizing them took place in a very short period of time, and it makes it very difficult.”

Local police had been inside the building that the shooter was on top of, Cheatle said. Federal law enforcement from the Secret Service were responsible for securing the inner perimeter away from that building.

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“In this particular instance, we did share support for that particular site and that the Secret Service was responsible for the inner perimeter,” Cheatle said. “And then we sought assistance from our local counterparts for the outer perimeter. There was local police in that building — there was local police in the area that were responsible for the outer perimeter of the building.”

Cheatle is scheduled to appear before the House Oversight Committee next Monday, July 22.