US President Donald Trump on Friday announced that the suspect had been taken into custody over the killing of right-wing activist Charlie Kirk after a massive manhunt.

"Somebody very close to him turned him in," Trump told Fox News in a live studio interview. He would go on to say that the suspect's father helped turn him in.

"The person was involved with law enforcement, but was a person of faith, a minister, and brought him to a US Marshal who was fantastic.

"They drove into the police headquarters, and he's there now."

He added: "We have the person that we think is the person we're looking for."

The gunman fired a single, fatal shot killing Kirk — a 31-year-old who rallied youth support for Trump — during an appearance at a Utah university on Wednesday. 

Hundreds of agents from across 20 law enforcement agencies were involved in the hunt.

Images released Thursday showed a man wearing Converse shoes, a black baseball cap, dark sunglasses and what appeared to be jeans, with a long-sleeved top emblazoned with a design that included an American flag.

Police say they believe the shooter fired from a rooftop up to 200 yards (180 meters) away, hitting Kirk in the neck.

Video footage showed a figure running across a roof at the university, then jumping to the ground and making his way off campus towards some trees — apparently the location where a high-powered bolt-action rifle was recovered.

Death penalty?

Utah Governor Spencer Cox said his state would pursue the death penalty over the case.

Reflecting the highly political nature of the killing, Kirk's coffin was transported to his home city of Phoenix on Vice President JD Vance's official plane.

Footage showed Vance with his hands on the casket as it was carried to Air Force 2.

Students at Utah Valley University on Thursday described their shock and their broader fears as political divisions deepen across the country.

Dave Sanchez told AFP witnessing the killing made him "sick to my stomach."

"We watch him all the time and so it really does feel like one of your own family members, your own brother's been killed," said Sanchez, 26.

In Orem Park, several hundred people wearing red MAGA caps and holding American flags attended a vigil on Thursday evening, where they prayed and held a moment of silence.

"It still feels insane that this happened," Jonathan Silva, 35, told AFP. "It's totally surreal."

Kirk, whom supporters have hailed as a "martyr," co-founded Turning Point USA in 2012 to drive conservative viewpoints among young people, with his natural showmanship making him a go-to spokesman on television networks.

The father-of-two used his audiences on TikTok, Instagram and YouTube to build support for anti-immigration policies, outspoken Christianity and gun ownership, and to spread carefully edited clips of his interactions during debates at his many college events.

The US right-wing media was in a state of grief and anger, with contributors recounting the impact Kirk had on their lives, but Trump has urged supporters to respond peacefully.