Maps show location of Trump and gunman at Pennsylvania rally shooting

New details are emerging on the investigation after a gunman opened fire Saturday at a rally in Butler, Pennsylvania, where former President Donald Trump was addressing a crowd of supporters. Trump was rushed from the stage after shots rang out, and later said he was injured by a bullet that struck the upper part of his right ear.

The gunman was killed by a Secret Service sniper, officials said. "U.S. Secret Service personnel neutralized the shooter, who is now deceased," the agency said in a statement.

A man in the audience at the rally was killed in the shooting, and two others were critically wounded.

Early Sunday morning, the FBI identified the gunman as Thomas Matthew Crooks, a 20-year-old  from Bethel Park, Pennsylvania, which is outside of Pittsburgh.

Multiple law enforcement sources said he was armed with a semi-automatic AR-style rifle and opened fire from the roof of a shed about 410 feet from the stage where Trump was speaking. The gunman's location was outside of the security perimeter established by the Secret Service around Trump's rally, according to law enforcement sources.

Satellite maps of the property where the rally took place, which were generated using GoogleEarth and include features to measure distance, appear to corroborate the distance of about 400 feet.

Secret Service snipers were positioned on a rooftop behind the stage where Trump was speaking. On Saturday, there were four counter-sniper teams on site, a law enforement official said.

The Bureau of Alcohol, Tobacco, Firearms and explosives was working to trace the weapon used in the shooting.

In a news conference late Saturday night, Kevin Rojek, the special agent in charge at the FBI's Pittsburgh branch, said he did not have information about any possible motive for the shooting. Rojek said that authorities are investigating the incident as an "attempted assassination."

Crooks has no known connection to foreign terrorism nor was he known to law enforcement prior to the rally, a law enforcement official said Sunday morning, but authorities were still looking into his background.

Rojek said at the briefing that the fact that the gunman could fire multiple shots was "surprising," but he did not respond to additional questions about the circumstances around the shooting itself or the FBI investigation.

Rojek did say that "there was identification of suspicious packages around where the shooter was, and so we deployed, in an abundance of caution, bomb assets, to make sure those were cleared for investigators," but did not say whether any suspicious packages were actually found.

"Right now, we're tracking down all leads, and doing all interviews, and tracking anything that we can regarding suspicious locations, vehicles ... that's all related to this event, but I can't confirm or deny anything beyond that," Rojek said.

Anthony Guglielmi, a spokesperson for the Secret Service, said in a statement that the agency had put protective measures in place for the rally.

Secret Service personnel were positioned around the stage and quickly rushed to surround Trump and usher him to his motorcade after the shooting.

"During Former President Trump's campaign rally in Butler, Pennsylvania, on the evening of July 13 at approximately 6:15 p.m., a suspected shooter fired multiple shots toward the stage from an elevated position outside of the rally venue. U.S. Secret Service personnel neutralized the shooter, who is now deceased," the Secret Service said in a statement Saturday. "U.S. Secret Service quickly responded with protective measures and Former President Trump is safe."

In another statement on Sunday, the Secret Service denied any suggestion that protective resources had been denied.

"The assertion that a member of the former President's security team requested additional security resources that the U.S. Secret Service or the Department of Homeland Security rebuffed is absolutely false. In fact, recently the U.S. Secret Service added protective resources and capabilities to the former President's security detail," Guglielmi said.

"The former President, and the current President, are commonly subject to threats.  The U. S. Secret Service takes threats seriously, and it takes actions based on those threats as warranted.  The U.S. Secret Service is constantly evaluating the very dynamic threat environment and responding to it in the fulfillment of its responsibilities."

While we can't get into specifics, the U.S. Secret Service adds additional resources for all campaign cycles including manpower and a variety of protective technology.  This addition of resources happens for all election cycles and is part of our candidate nominee operations section, also known as CNOS."

The former president and his campaign team released initial statements after the shooting to acknowledge what happened and thank law enforcement for their response. Trump shared a new statement on social media Sunday morning saying, "I truly love our Country, and love you all, and look forward to speaking to our Great Nation this week from Wisconsin," where the Republican National Convention is scheduled to begin Monday.

"In this moment, it is more important than ever that we stand United, and show our True Character as Americans, remaining Strong and Determined, and not allowing Evil to Win," Trump said.

Pat Milton, Nicole Sganga and the CBS News Confirmed team contributed reporting.