Sen. Josh Hawley, R-Mo., said Monday that a whistleblower had come forward to his office claiming there was supposed to be a security officer posted on the roof of the building where the gunman fired from, but that that person abandoned the post due to the heat.
The whistleblower, who Hawley said has direct knowledge of the Secret Service's planning for the event, alleged "that there was supposed to be a law enforcement presence on the roof that day," Hawley wrote in a letter to Department of Homeland Security Secretary Alejandro Mayorkas posted on X. "In fact, the whistleblower alleges that at least one individual was specifically assigned to the roof for the duration of the rally, but this person abandoned his or her post due to the hot weather."
Hawley said the whistleblower also alleged that "concerns over the heat prompted law enforcement to forego patrolling" the building and instead station security personnel inside it.
Hawley's letter requests that Mayorkas address the whistleblower's allegations by Friday.
ABC News has reached out to the Secret Service for comment on the letter.
During a hearing before the House Oversight Committee on Monday, Secret Service Director Kim Cheatle said that there was "overwatch" provided for the roof, but did not elaborate, when asked why no agents were placed on the building.
"What I can tell you is that there was a plan in place to provide overwatch, and we are still looking into responsibilities and who was going to provide overwatch," Cheatle said. "But the Secret Service in general, not speaking specifically to this incident, when we are providing overwatch, whether that be through counter-snipers or other technology, prefer to have sterile rooftops."
-ABC News' Allison Pecorin