A young Utah man suspected of killing the influential conservative activist Charlie Kirk at a university in the city of Orem was in custody today, Utah Governor Spencer Cox told said.
"We got him," Mr Cox told reporters.
Mr Cox identified the suspect as Tyler Robinson and said the arrest was made after one of Mr Robinson's relatives contacted a friend, who then contacted the police.
"On the evening of September 11th, a family member of Tyler Robinson reached out to a family friend, who contacted the Washington County sheriff's office with information that Robinson had confessed to them or implied that he had committed the incident," Mr Cox said.
A family member interviewed by investigators said Mr Robinson had become more political recently and spoke in a disparaging manner about Mr Kirk, Mr Cox told reporters.
Mr Robinson was taken into custody last night, about 33 hours after Mr Kirk's murder, FBI Director Kash Patel said at the press conference.
Mr Kirk, a close ally of US President Donald Trump, was killed by a single bullet as he spoke onstage at an outdoor amphitheatre at Utah Valley University on Wednesday.
"I think we have him," Mr Trump told Fox News in an interview earlier today.
Previously, US investigators said they had found the bolt-action rifle believed to have been used to kill Mr Kirk and released images of a person of interest.
The FBI had circulated grainy images apparently taken from security cameras showing a "person of interest" wearing a black top, black sunglasses and a dark baseball cap.
Mr Kirk, an author, podcast host and close ally of Mr Trump, helped build the Republican Party's support among younger voters.
FBI and state officials said the killer arrived on the campus a few minutes before the start of the event, a debate led by Mr Kirk titled "Prove Me Wrong" in front of 3,000 people at Utah Valley, about 65km south of Salt Lake City.
Security camera videos showed a person going up stairwells to gain access to a roof before firing at Mr Kirk, the officials said at a press briefing.
Mr Kirk, a staunch defender of gun rights, was answering an audience question about mass shootings when the bullet struck his neck. Audience members fled in panic.
The shooter jumped off the roof and fled into an adjoining neighbourhood, said Robert Bohls, an FBI special agent in charge.
Investigators found a "high-powered, bolt-action" rifle in a nearby wooded area, and were examining that along with palm prints and footprints for clues.
Watch: Moment suspected gunman flees scene of shooting
Yesterday, with classes cancelled, the roof of the building on the otherwise deserted campus and the nearby woods were strung with yellow tape as investigators scoured them for evidence.
Mr Kirk - the co-founder and president of the conservative student group Turning Point USA - appeared at Utah Valley on Wednesday as part of a planned 15-event "American Comeback Tour" of US college campuses.
His killing stirred outrage and denunciations of political violence from Democrats, Republicans and foreign governments.
Mr Trump said he would award Mr Kirk the Presidential Medal of Freedom, the nation's highest civilian honour.
Mr Kirk, who was married and the father of two young children, was celebrated by Republicans as a charismatic advocate for right-wing policies on race, gender, immigration, religion and gun regulation.
He frequently engaged with his critics from the far left to the far right, often inviting members of his audiences to debate him live.
