Firing at the GOP presidential candidate during a campaign rally in Butler, Pa., the gunman killed one person in the crowd and critically injured two others. One of the bullets grazed Trump’s ear.

The joint Senate hearing offered fresh details about the first attack in decades on a U.S. leader under Secret Service protection, which has sparked multiple investigations and forced a reckoning over how to protect high-profile political candidates during a fraught campaign season.

An independent panel investigating the security failures started this week and will wrap up its review by the beginning of October, the Department of Homeland Security said in a statement Tuesday.

Secret Service Director Kimberly Cheatle resigned last week under pressure from lawmakers who excoriated her performance because of the attack and what they saw as her failure to answer their questions. On Tuesday, her interim successor outlined how the agency plans to change its protective posture at campaign rallies and improve coordination with local law enforcement partners.

At various moments, the hearing for members of the Senate Homeland Security and Governmental Affairs Committee and the Senate Judiciary Committee turned emotional and even angry, particularly when Sen. Josh Hawley (R-Mo.) loudly called for Secret Service personnel to be ousted from the agency.

“Sir, this could have been our Texas schoolbook depository,” Rowe told the lawmaker, referring to the 1963 assassination of President John F. Kennedy. “I have lost sleep …”

“Then fire somebody,” Hawley hollered at him.

Raising his voice in response, Rowe said he would let the investigation play out before delivering punishments.

“I will tell you, Senator, I will not rush to judgment,” Rowe said. “This was a failure, and we will get to the bottom of it.”

Rowe separately rebuked Sen. Roger Marshall (R-Kan.), who suggested that the Secret Service may have “a cultural problem or gross incompetence.”

“Senator, I know you’re not calling our workforce incompetent,” Rowe retorted.

A veteran agent who served on the presidential protective detail during President George W. Bush’s second term, Rowe told lawmakers that he visited the rally site after the attempted assassination.

Rowe said he lay prone on the rooftop from which the 20-year-old gunman, Thomas Matthew Crooks, fired eight shots from an AR-style rifle, so he could see for himself the clear view Crooks had of Trump.

“What I saw made me ashamed,” said Rowe, who previously served as deputy director of the Secret Service, responsible for overseeing daily investigative and protective operations.

Raising his voice in frustration, Rowe showed lawmakers oversized photos of the rooftop, near where officials have said local law enforcement officers were posted.

“I cannot understand why there was not better coverage” of that roof, Rowe said. “I think this was a failure of imagination, a failure to imagine that we actually do live in a very dangerous world where people do actually want to do harm to our protectees. I think it was a failure to challenge our own assumptions.”

Rowe said the Secret Service assumed there would be “sufficient eyes” from local law enforcement covering the outer perimeter of the rally, including countersniper teams in the American Glass Research (AGR) building from which the shooter fired.

“We assumed that the state and locals had it,” Rowe said in response to questioning from Sen. John Cornyn (R-Tex.). “I can assure you that we’re not going to make that mistake again.”

Going forward, Secret Service counter-snipers will join local counter-snipers on roofs and other locations, Rowe said, similar to the way they handle security at the United Nations General Assembly in New York. “I’ve directed that when we’re talking to people and we’re making requests, that we are very specific about what we want, we are providing explicit instructions,” he told lawmakers.

Rowe also said the Secret Service will use more drones around such events and improve radio communications between the Secret Service and other law enforcement agencies that contribute to their security.

Lawmakers at the hearing, particularly Republicans, criticized the Secret Service over the failure to stop the gunman from climbing onto the roof just outside the rally’s security perimeter, and they suggested that Cheatle’s resignation was not enough.

Sen. Gary Peters (D-Mich.), chairman of the Homeland Security Committee, said Congress needs answers “about what appears to be a problematic communications system” used by the Secret Service.

Before the shooting, local police assisting with security at the event had spotted the suspicious young man, but much of that information was not relayed to the Secret Service agents who are part of the former president’s security detail.

FBI Deputy Director Paul Abbate said that while investigators still don’t have a sense of the gunman’s motive, they have recently discovered a set of online posts possibly made by him in 2019 and 2020 that reflect “antisemitic and anti-immigration themes” and espouse political violence.

“This was just discovered, and it is being closely analyzed right now,” Abbate said, cautioning that agents still need to verify that the posts were made by the gunman.

Previously, investigators briefly thought an online post about the date of the assassination was made by the shooter, before deciding that it was not.

Abbate said that if the posts do turn out to have been written by Crooks, “it is the first indication that he is expressing … extremist views and talking about political violence.”

Sen. Rick Scott (R-Fla.) chided agency officials for not speaking in public more often about what happened and what investigators have found.

“You’ve allowed the public to assume the negative, which I don’t get. I think you should have been doing all along at least once-a-day press conferences. I think you’ve got to tell the public what’s going on,” said Scott. “You ruin your reputation, impact the integrity of the federal government; it makes no sense to me.”

Abbate offered the most complete official timeline yet of the days leading up to the attack, and the gunman’s activities before then.

He said Crooks registered to attend the Trump rally on July 6, three days after the event was announced, and searched online that day for “How far was Oswald from Kennedy?” — a reference to the Kennedy assassination by Lee Harvey Oswald.

On the morning of the rally, Crooks visited the Butler site and bought ammunition. At 3:51 p.m., he flew a drone about 200 yards from the rally grounds for 11 minutes.

The Secret Service did not detect the drone because of cellular connectivity problems in the area that hobbled their own aerial operations, Rowe acknowledged at the hearing.

Local law enforcement first noticed Crooks at 4:26 p.m., identified him as “suspicious” at 5:10 p.m., and sent his photo to local SWAT operators in a text message group around 5:38 p.m., Abate said.

Officers lost sight of him from 6:02 p.m. to 6:08 p.m. Crooks clambered atop the roof at 6:06 p.m., according to video from a local business.

Two more minutes passed before local law enforcement spotted him there.

At 6:11 p.m., a local police officer was boosted from the ground by another officer to peek at the roof, saw the shooter, and radioed that he was armed with a long gun.

In the next 30 seconds, shots were fired.

Samuel Oakford contributed to this report.