Rally gunman was only around 450 feet away from Donald Trump as he opened fire

• Former US President Donald Trump survived an assassination attempt at a rally in Pennsylvania.
• The gunman was on an elevated surface around 450 feet away from his target.

The gunman who shot at Donald Trump was only about 450 feet (roughly 137 meters) away from the former US president, satellite imagery shows.

Trump was speaking at a rally in Pennsylvania on Saturday when gunshots rang out, and he was swarmed by Secret Service agents.

The former president emerged from the incident with a bloodied ear as the agents ushered him away.

The FBI has since identified 20-year-old Thomas Matthew Crooks of Bethel Park, PA, as the shooter.

Crooks "fired multiple shots toward the stage from an elevated position," according to a statement shared by Secret Service spokesperson Anthony Guglielmi.

The Associated Press geolocated a video on social media showing a man in gray camouflage lying motionless on the roof of a manufacturing plant just north of where the rally took place.

The shooter could have reasonably struck Trump from that distance.

US Army recruits are trained to hit human-sized targets 150 meters away with an M-16 rifle, the AP reported. The AR-15, which the shooter reportedly used, is the civilian version of the military-grade M-16, per the report.

Members of Trump's Secret Service stood around 440 feet (or about 134 meters) away from Crook, per the satellite images.

When asked whether law enforcement was unaware of the shooter's presence until shots were fired, Kevin Rojek, an FBI Special Agent, said: "That is our assessment at this time."

Matt Shoemaker, a former intelligence officer at the Defense Intelligence Agency, called the incident a "major failure" of the Secret Service.

"I've been to these sorts of events before, and there are layers upon layers of security," Shoemaker said. "So for the alleged shooter to be on a rooftop, with a clear shot to the podium — it is mind-boggling to say that this was overlooked."

Tim McCarthy, who in 1981 defended then-President Ronald Reagan from a gunman, agreed that the incident represented a failure by the service.

"Any time a protectee is harmed, there's something that has to change," McCarthy told Chicago-based outlet WGN-TV. "You have to critically look at what happened, why it happened, and how it can be prevented in the future."