Trump shooting motive unknown three days after assassination attempt

• The motive of the 20-year-old gunman who tried to assassinate former President Donald Trump remained unknown three days after the shooting at a campaign rally in western Pennsylvania.
• More than a dozen guns were found by authorities in a search of the home of the shooter, Thomas Crooks.
• The U.S. Secret Service continues to face questions about how Crooks was able to crawl up to a roof overlooking the site of Trump's rally.

The motive of the 20-year-old gunman who tried to assassinate former President Donald Trump remained unknown three days after the shooting at a campaign rally in western Pennsylvania.

Information analyzed from a phone belonging to the gunman, Thomas Crooks, has not helped the FBI determine what led him to fire a rifle multiple times at Trump and other rally attendees Saturday afternoon before he was killed by a Secret Service sniper, a senior law enforcement official told NBC News.

More than a dozen guns were found by authorities in a search of the Crooks family home.

Two suspected improvised explosive devices were found in Crooks' car near the rally, while a third suspected IED was found at his home.

A joint intelligence bulletin issued by the FBI and Department of Homeland Security warned that extremists may conduct attacks in retaliation for the assassination attempt, a source told NBC News.

 "The FBI and DHS remain concerned about the potential for follow-on or retaliatory acts of violence following this attack, particularly given that individuals in some online communities have threatened, encouraged, or referenced acts of violence in response to the attempted assassination," the bulletin said, according to the source.

That same bulletin confirmed that Crooks purchased 50 rounds of ammunition at a