The Department of Homeland Security's inspector general says it has opened up an investigation into the U.S. Secret Service's handling of security for former President Donald Trump on the day a gunman tried to assassinate him at a Pennsylvania rally.

In a brief notice posted to the inspector general's website, the agency said the objective of the probe is to "Evaluate the United States Secret Service's (Secret Service) process for securing former President Trump's July 13, 2024 campaign event."

There was no date given for when the investigation was launched. The notice was among a long list of ongoing cases that the inspector general's office is pursuing.

President Joe Biden already had directed an independent review of the security at the rally.

The shooting has raised questions about how the gunman was able to climb onto a roof with a clear line of site to the former president, who was injured.

The 20-year-old shooter, Thomas Matthew Crooks, was able to get within 135 meters (157 yards) of the stage where the Republican former president was speaking when he opened fire. That's despite a threat on Trump's life from Iran leading to additional security for the former president in the days before the Saturday rally.

A bloodied Trump was quickly escorted off the stage by Secret Service agents, and agency snipers killed the shooter. Trump said the upper part of his right ear was pierced in the shooting. One rallygoer was killed, and two others critically wounded.

Secret Service Director Kim Cheatle said the agency understands the importance of the review ordered by Biden and would fully participate in it as well as with congressional committees looking into the shooting. She said the agency was working to understand how Saturday's shooting happened and to make sure something like it never does again.

The agency of roughly 7,800 staff members is responsible for protecting presidents, vice presidents, their families, former presidents, their spouses and their minor children under the age of 16 and a few other high-level Cabinet officials such as the Homeland Security secretary.