As authorities tried to unravel the motive and details of the case, sources said investigators were looking at whether Routh was frustrated with Trump's position on Ukraine. Trump refused to answer when asked if Ukraine should win its war against Russia during the ABC News presidential debate last week.
Authorities recovered an "AK-47-style" rifle with a scope, two backpacks -- one of which had a ceramic tile in it -- and a GoPro from the scene, Palm Beach County Sheriff Ric Bradshaw said. The would-be gunman was within 300 to 500 yards of Trump when he was spotted. The former president was unharmed in the incident and it is unclear whether the suspect fired any shots.
Routh's vehicle was stopped by police after a witness reported his license plate number to authorities. He was placed into custody on Sunday afternoon. Authorities expect to file charges relating to the incident in the coming days, sources told ABC News. The suspect's motive remains unknown.
Routh is believed to have ties to North Carolina and Hawaii, according to sources. The FBI is conducting an extensive investigation into Routh's social media activity, travel and any criminal record, sources said. Friends, family and associates are also being sought for interviews.
A law enforcement source told ABC News that profiles on X, LinkedIn, and Telegram are under investigation for a possible connection to Routh. Routh also appears to have operated a Facebook page, which has now been removed, and which listed the same phone number shared on his apparent X profile.
When ABC News dialed that number, an answering machine message said: "This is Ryan with Camp Box Buildings in Hawaii, and also the National Volunteer Center sending soldiers to Ukraine as well as Taiwan."
Online, he appears to have been a prolific booster of several causes, chiefly of Ukraine's, with numerous posts referring to an effort to recruit soldiers for that country. Specifically, many of Routh's posts referred to an effort to send Afghan soldiers to Ukraine.
It was not immediately clear whether Routh had actually recruited any fighters for Ukraine or whether he had any contact with Ukraine's military or government.
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Routh's apparent X profile contained dozens of posts calling on politicians, celebrities and journalists to support Ukraine. In 2022, shortly after Russia's full-scale invasion, posts on that profile contained claims that Routh had traveled to Kyiv.
Routh spoke with an ABC News team in the Ukrainian capital Kyiv on April 30, 2022 -- two months into the war -- at a protest held by family members of Azov Battalion soldiers defending the city of Mariupol against Moscow's forces.
He was wearing an American flag bandana around his neck and was holding a handwritten sign that read: "Please world we need everyone here. This is good against evil. These children want normal lives ... End Russia for our kids."
Routh told The Financial Times that he had tried to join Ukraine's International Legion for the Defense of Ukraine -- which is made up of foreign volunteers -- but was rejected as too old. Routh claimed the Legion then suggested he work to recruit other foreigners to serve in the unit.
The International Legion for the Defense of Ukraine told ABC News via email: "We would like to clarify that Ryan Wesley Routh has never been part of, associated with, or linked to the International Legion in any capacity. Any claims or suggestions indicating otherwise are entirely inaccurate."
A March 2023 post on a LinkedIn profile appearing to belong to Routh contained two undated photos of Routh, respectively showing him in front of the U.S. Congress and at Kyiv's Independence Square. The post was captioned, "In DC and Kyiv to provide soldiers for the war effort."
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On June 10, 2020, Routh's apparent X profile directed a post on X at Trump in which he said had supported Trump in the 2016 presidential election but that Trump had become a "disappointment." The post concluded, "I will be glad when you are gone."
Several X posts in March 2020 referred to support for then-Democratic presidential primary candidates Sen. Bernie Sanders and Rep. Tulsi Gabbard. Posts in January 2024 indicated support for former Republican presidential primary candidate Vivek Ramaswamy.
Facebook posts from October and November 2023 promoted conspiracy theories about China, COVID-19 and biological warfare. In December, Routh posted to the platform questioning the historical claim of Jewish people to Israel.
Routh's apparent phone number was also listed on a website for a so-called "Taiwan Foreign Legion," which calls on international volunteers to fight for Taiwan in the event of a possible conflict with China.
The most recent post on Routh's apparent Facebook page also refers to an effort to convince Taiwan to accept Afghan fighters.
ABC News' Pierre Thomas, Josh Margolin, Luke Barr, Aaron Katersky, Jack Date, Peter Charalambous, Alexander Mallin, Leah Sarnoff, Joe Simonetti, Helena Skinner and Zohreen Shah contributed to this report.