Live Updates: Trump rally shooting investigation continues as new details emerge about assassination attempt

An investigation is continuing into the assassination attempt on former President Donald Trump, who appeared at the Republican National Convention in Milwaukee Monday night — the first time he has been seen in public since he was shot and injured at his campaign rally in Pennsylvania. 

The crowd at the convention cheered Trump, whose ear was bandaged after it was hit by a bullet on Saturday.

Trump also showed up at the convention on its second night. Increased security around him was noticeable, with agents walling him off.

Details are emerging about the moments that led up to the shooting. Bystanders alerted law enforcement to a gunman on the roof of a building about 410 feet away from the stage at least two minutes before the first shot was fired at Trump, video analyzed by CBS News shows. 

A sniper from a local tactical team deployed to assist the U.S. Secret Service at the rally took a picture of the gunman and saw him looking through a rangefinder minutes before he tried to assassinate the former president, a local law enforcement officer with direct knowledge of the events told CBS News. 

The sniper was one of three members of local tactical teams who were stationed inside the building that the shooter used in the attack, the officer said. The operations plan had them stationed inside, looking out windows toward the rally, scanning the crowd. The details about the three snipers were first reported by the local news outlet BeaverCountian.com. 

The FBI is investigating whether the shooter — Thomas Matthew Crooks —  was a politically motivated homegrown domestic violent extremist, and investigators are still combing through his background. Justice Department officials told reporters that investigators have the shooter’s phone and were examining it at the FBI lab in Quantico, Virginia.

A federal law enforcement bulletin obtained by CBS News identified the gunman as “an apparent lone attacker,” warning violent extremists could try to conduct “follow-on or retaliatory” attacks over the next few months, related to November’s election. 

The gunman killed Corey Comperatore, a firefighter. Trump and two others — 57-year-old Marine Corps veteran David Dutch and 74-year-old James Copenhaver — were wounded.