The suspected gunman who attempted to assassinate former President Donald Trump at his campaign rally Saturday purchased 50 rounds of ammunition ahead of the event, according to a bulletin from the Department of Homeland Security and the FBI Monday.

Thomas Matthew Crooks purchased the rounds from a gun and ammunition shop in Bethel Park, Pennsylvania, according to officials.

The bulletin notes that two improvised explosive devices were found in the shooter's car and one at his home.

"Over the last several months, Crooks received several packages, including some marked as possibly containing hazardous material, according to a review of his shipping history," officials wrote.

Officials also warn of future "follow-on or retaliatory acts of violence in response to this assassination attempt."

"We cannot rule out the possibility that some DVEs (Domestic violent extremists) or other actors may attempt follow-on or retaliatory acts of violence in response to this assassination attempt."

Eric Trump said there is "no question" that a Trump family member will attend the funeral of Corey Comperatore, who was shot and killed at the campaign rally on Saturday.

During an interview with Fox News on Monday night at the Republican National Convention, Eric called Comperatore's death "unthinkable," adding, "This is a person who loved Donald Trump, his family. He jumped on his children. It's unthinkable what happened there."

Comperatore, 50, was a firefighter and a father of two daughters, Pennsylvania Gov. Josh Shapiro said Sunday. He was from Sarver, Pennsylvania.

Comperatore "died a hero" when he "dove on his family" to protect them from the gunfire during the rally, his wife said, according to Shapiro.

Eric Trump said that the GoFundMe page created for Comperatore's family was close to reaching $5 million.

Former President Donald Trump shared an update with ABC News' Jonathan Karl on how his right ear is recovering and said the assassination attempt at his campaign rally Saturday had "impact."

When asked if the close call to the bullet striking his head "changed him," Trump said, "I don't like to think about that, but, yes, I think has an impact."

Trump said his ear is doing fine and that he hopes the bandage will be off by the time he speaks on Thursday at the Republican National Convention.

Donald Trump spoke with ABC News' Jonathan Karl over the phone on Monday for a 10-minute conversation, touching on his phone call with President Joe Biden after the assassination attempt Saturday.

"It was very nice," Trump said. "He couldn't have been nicer."

He then marveled at the people who called him after the assassination attempt - including very prominent people who have been harshly critical of him.