Trump Jr. says father is 'changed man'

Authorities "have not identified an ideology associated" with the suspected shooter, Thomas Crooks, FBI Pittsburgh Special Agent in Charge Kevin Rojek told reporters on a call on Sunday.

"We're looking into his background, his day-to-day activities, any writings and social media posts that might help us identify what led to this shooting. And we have not seen anything threatening," Rojek said.

Crooks had no known mental illness history, he said.

Crooks' family is cooperating with federal authorities, officials said.

Officials told reporters they don't have any insights on what the suspect's actions were prior to opening fire at the shooting site, but said it's something they are investigating.

The FBI has received more than 2,000 tips, according to Rojek.

Crooks' gun and phone will be transported to the FBI lab in Quantico, Virginia, officials said.

Rojek also confirmed there was a suspicious device that was found in the suspect's car and said the FBI is still analyzing what it is. Another device was found in the suspect's home, according to the FBI. Rojek described both the devices as rudimentary.

The FBI is seeing an increase of violent threats online in the aftermath of the assassination attempt, FBI Deputy Director Paul Abbate said.

"We've seen individuals go online and attempt to mimic or pose as the shooter who obviously is now deceased," Abbate said. "We're also focused on the continuing efforts, which were already substantial, given that there are national special security events on the upcoming conventions in Chicago, in Milwaukee, to work with Secret Service in the lead to play our part in protecting the people and the facilities and events there, as well."

FBI Director Christopher Wray called the assassination attempt an "attack on our democracy."

"An attempt to assassinate a presidential candidate can only be described as absolutely despicable and will not be tolerated in this country," Wray told reporters.

-ABC News' Pierre Thomas, Aaron Katersky, Jack Date and Luke Barr

The man suspected of shooting Donald Trump previously sought to join his high school's rifle club, but was rejected and asked not to return, two students who were members of the team at the time told ABC News.

The suspect, Thomas Crooks, attended what was described as "preseason" for the rifle club, which is held before tryouts, but he did not make it to the tryouts, the two team members said. Both students said Crooks was a "bad shot," with one adding that he wasn't the right "fit."

"He didn't just not make the team -- he was asked not to come back because how bad of a shot he was. It was considered like, dangerous," classmate Jameson Myers told ABC News.

"On the first day of preseason, he basically couldn't even hit the target," Myers said.

The team's coach declined to comment and referred questions to the school district. A spokesman for the school district did not immediately respond to a request for comment.

READ MORE | Suspected Trump rally shooter was rejected from high school rifle club, two former team members say

The two people injured in Saturday's shooting have been upgraded from critical condition to stable condition, according to the Pennsylvania State Police.

Police identified 57-year-old David Dutch, of New Kensington, Pennsylvania, and 74-year-old James Copenhaver, of Moon Township, Pennsylvania, as the injured shooting victims.

The two people who were critically wounded in the assassination attempt on former President Donald Trump have been identified.

Killed in the shooting was Corey Comperatore, 50, of Sarver, Pennsylvania.

Pennsylvania Gov. Josh Shapiro has ordered flags to be flown at half-staff in honor of Comperatore, a firefighter who leaves behind a wife and two daughters.

The U.S. Secret Service is investigating how a gunman armed with an AR-style rifle was able to get close enough to shoot and injure former President Donald Trump at a rally Saturday in Pennsylvania, a monumental failure of one of the agency's core duties.

The gunman, who was killed by Secret Service personnel, fired multiple shots at the stage from an "elevated position outside of the rally venue," the agency said.

READ MORE | The Secret Service is investigating how a gunman who shot and injured Trump was able to get so close