A law enforcement officer was supposed to be stationed on the roof of the building used by former President Trump’s would-be assassin Thomas Crooks during the rally on July 13, but he didn’t show up for work that day, according to former Secret Service agent Dan Bongino.

The popular conservative talk radio host made the stunning claim during a discussion with Tucker Carlson, David Sacks, and Donald Trump Jr. at the Republican National Convention in Milwaukee, Wisconsin, Tuesday.

Bongino said an “unimpeachable source” told him someone was assigned to man the roof of the American Glass Research building in Butler, Pennsylvania, but the officer “didn’t show up.”

“That post, according to my source, that roof was supposed to be a police post… [there] was supposed to be someone there,” he said. “They’re now making up excuses saying the pitch of the roof … My source says to me that no one knows why the post didn’t show up.”

Bongino said Secret Service Director Kimberly Cheatle’s claim that the roof was left unmanned because it was too slanted was a “nonsense story” being fed to the media.

“I was also told that the Secret Service director has been given instructions from the administration and the DHS secretary: ‘If you wanna keep your job, you’ll keep your mouth shut about this,'” he added.

“They’re not putting it out there, but if you get those site post logs and those police instructions and there was a post on there and they didn’t show up and no one checked—someone could have got your dad killed within a millimeter,” Bongino told Don Jr.

House Republicans are conducting a full investigation into the security failures surrounding the assassination attempt against Trump, saying there are many questions and Americans need answers.

Cheatle has been called to appear before the House Oversight Committee for a hearing on the security failure on July 22.

And the House Judiciary Committee announced on Wednesday that they will hold a hearing with FBI Director Christopher Wray on July 24 to examine the Bureau’s investigation into the assassination attempt.