A suspect in the fatal shooting of conservative activist Charlie Kirk at a Utah university has been taken into custody, US President Donald Trump says, ending an intense manhunt that followed what Trump described as a "heinous assassination".

Kirk's killer had eluded police and federal agents for more than 24 hours after Wednesday's shooting, in which a sniper fired a single gunshot that killed Kirk, 31, during an appearance at Utah Valley University in Orem.

"I think we have him," Trump told Fox News in an interview, adding that a person who knows the suspect had turned him in.

"I think with a high degree of certainty we have him in custody."

Trump did not share the suspect's identity.

Trump did not share the suspect's identity. Investigators were due to brief journalists later on Friday.

The suspect was in the custody of Utah state law enforcement, a person familiar with the investigation said, asking for anonymity.

Previously, US investigators said they had found the bolt-action rifle believed to have been used to kill Kirk and released images of a person of interest.

Trump said earlier ‘they’re making great strides’ on finding Charlie Kirk’s assassin. – AP

The FBI had circulated grainy images apparently taken from security cameras showing a person wearing a black top, black sunglasses and a dark baseball cap. The long-sleeved top appears to have been emblazoned with an image of a bald eagle flying across a US flag.

Law enforcement officials also released video of the shooter running across the roof and lowering himself on to the ground.

"Somebody this close recognizes even a little tilt of the head, which nobody else would do," Trump said in the interview.

Investigators have yet to publicly discuss any motive, but Trump told reporters that he had an indication of the killer's motivation."We'll let you know about that later," he said, adding that law enforcement was making "big progress" in the investigation.

FBI and state officials said the killer arrived on the campus a few minutes before the event began, a debate led by Kirk titled "Prove Me Wrong" outdoors in front of about 3000 people at Utah Valley University in Orem, Utah, about 40 miles (65km) south of Salt Lake City.

Security-camera videos show a person going up stairwells to get onto a roof before firing at Kirk, the officials said.

FBI release photos of person of interest in Kirk shooting and offer $100k reward. – AP

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 FBI offered a $100,000 reward for information leading to the killer's arrest and circulated grainy images taken from security cameras showing a "person of interest" wearing a black top, black sunglasses and a dark baseball cap. The long-sleeved top was emblazoned with an image of a bald eagle flying across a US flag.

A second batch of photos released by Utah state officials showed slightly clearer images of the slender young man, revealing greater details of his backpack and Converse shoes.

Officials also released video of a man climbing down off the roof from where the sniper fired the fatal round.

That person left a palm imprint and other DNA materials on the building as he dropped down to the ground, Utah Department of Public Safety Commissioner Beau Mason said.

"There's a shoe imprint where we believe the suspect is clearly identified as wearing Converse tennis shoes," Mason added.

Utah governor pleads for public's help in finding person who shot Charlie Kirk on university campus. – AP

The video also showed the man crossing a street and moving into a wooded area near campus, which is where authorities said they found a "high-powered, bolt-action" rifle.

The shooter has not been publicly identified, though lawmakers, commentators and online sleuths have already filled social media and message boards with speculation and blame-casting about the killer's ideology.

Utah Governor Spencer Cox appealed to the public for help.

“We cannot do our job without the public’s help right now,” he said.

"So far, we've received more than 7,000 leads and tips. I would just note that the FBI hasn't received this many digital media tips from the public since the Boston Marathon bombing" of 2013.

FBI Director Kash Patel travelled to Utah and appeared at a press briefing with state and federal officials, but did not speak.

Memorial for Charlie Kirk set up outside Turning Point headquarters. – AP

Kirk – co-founder and president of the conservative student group Turning Point USA – was appearing at the Utah university 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 Republicans, Democrats and foreign governments.

Trump said he would award Kirk the Presidential Medal of Freedom, the nation's highest civilian honour.

US Vice President JD Vance cancelled his trip to New York to commemorate the attacks by al Qaeda on September 11, 2001, and instead travelled to Utah to see Kirk's family and to fly them and Kirk's casket home to Arizona aboard Air Force Two.

Kirk began his career in conservative and right-wing politics as a teenager, which he has described as shaped by his Christian faith.

A little more than a decade later, some of the friends he made along the way are now at the highest levels of US government and media, with Vance recalling that he was in multiple group chats with Kirk.

"So much of the success we've had in this administration traces directly to Charlie's ability to organise and convene," Vance wrote in a tribute posted on social media. 

"He didn't just help us win in 2024, he helped us staff the entire government."

Kirk's organisation, Turning Point USA, said in a statement that its co-founder had believed in "the power of argument and good-faith debate" and had received thousands of threats.

The shooting punctuated the most sustained period of US political violence since the 1970s.

Reuters has documented more than 300 cases of politically motivated violent acts across the ideological spectrum since supporters of Trump attacked the US Capitol on January 6, 2021.

Trump himself has survived two attempts on his life last year, one that left him with a grazed ear during a campaign event and another two months later foiled by federal agents. Two people were detained, questioned and released, but neither was a suspect, the FBI said.

Democratic leaders on Capitol Hill call for unity after killing of conservative activist Charlie Kirk. – AP

Kirk, who was married and the father of two young children, published his most recent book last year calling for a "Right Wing Revolution" and had just returned from a speaking tour in South Korea and Japan.

He was championed by Republicans as a charismatic advocate for right-wing policies on race, immigration, religion and gun regulation who frequently engaged with his critics from the far left to the far right, often inviting members of his audiences to debate him live.

Trump told reporters that he had spoken with Kirk's wife, Erika Frantzve, "she's devastated, she's absolutely devastated, as you can imagine".