After an attempted assassination of former President Donald Trump at a campaign rally in Pennsylvania over the weekend, officials are calling for an investigation into security lapses at the event.

A gunman perched on the roof of an elevated building outside the official rally venue shot Trump with a rifle, clipping his ear. The gunman killed one rally attendee in the crowd and critically injured two others.

The alleged gunman, 20-year-old Thomas Matthew Crooks,  was killed by the Secret Service on the scene less than a minute after the shooting occurred.

The weapon used by the gunman was legally purchased in 2013 by Crooks’ father, but the suspect purchased ammunition at a local gun store just hours before the shooting, The Washington Post reported.

Current sitting presidents typically have more protection and security than former presidents and candidates, regardless of their high profile. Stephen Colo, a former top-level Secret Service assistant director, said he was surprised that a counter-sniper team was part of the security at the event, WFAA reported.

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Former Secret Service agent Timothy McCarthy raised questions regarding the security failure at the rally, commenting that the Secret Service had “better be doing a deep dive into what happened there and doing whatever it takes to figure it out.”

“How did that person get up on that building?” McCarthy asked. “How did that happen? I mean, that’s the key to the entire thing. And what measures were put in place to prevent it?”

In a press briefing on Sunday, President Joe Biden, Trump’s main political opponent, called for unity.

“Unity is the most elusive goal of all, but nothing is more important than that right now.”

Biden ordered an independent review of the security measures at the rally last Saturday and asked the Secret Service to review its security measures for the Republican National Convention in Milwaukee this week.

Kimberly Cheatle, Secret Service director, also addressed concerns about RNC security.

“The security plans for National Special Security Events are designed to be flexible. As the conventions progress, and in accordance with the direction of the President, the Secret Service will continuously adapt our operations as necessary in order to ensure the highest level of safety and security for convention attendees, volunteers, and the City of Milwaukee,” Cheatle said.

“In addition to the additional security enhancements we provided former President Trump’s detail in June, we have also implemented changes to his security detail since Saturday to ensure his continued protection for the convention and the remainder of the campaign,” she added.

During a press briefing shortly after the assassination attempt, the FBI special agent in charge of the Pittsburgh Field Office, Kevin Rojek, said that the gunman’s motive was still unclear, but the FBI and state and local law enforcement will continue the investigation.