Tyler Robinson, the 22-year-old Utah man accused of assassinating conservative activist Charlie Kirk, was charged with aggravated murder on Tuesday, a prosecutor said, adding that Robinson left DNA on the trigger of the rifle that fired the fatal shot.
The charge means Robinson could face the death penalty if he is convicted of killing Kirk last week at Utah Valley University in Orem.
"The murder of Charlie Kirk is an American tragedy," Utah County Attorney Jeff Gray said in announcing the charges.
Kirk was shot and killed on September 10 as he spoke with students during one of his regular campus talks and died soon after.
Prosecutors allege Robinson shot Kirk in the neck with a bolt-action rifle from the roof of a nearby campus building.
A Utah Valley University police officer was watching the university campus crowd from an "elevated position" and identified the roof of the Losee Centre as a potential position for a shooter, Gray said.
The officer found evidence on the roof immediately, he said, and spurred officers to direct their attention to surveillance video leading to the roof.
Gray said Robinson's DNA was found on the trigger of the rifle, which he said Robinson discarded before asking his roommate to conceal evidence.
Robinson left a note under a keyboard saying he planned to kill Kirk and confessed after the shooting, documents show.
Robinson was also charged with felony discharge of a firearm, punishable by up to life in prison, and obstructing justice, punishable by up to 15 years in prison.
He was scheduled to appear on camera for a virtual court hearing on Tuesday afternoon.
It was unclear whether Robinson had an attorney who could speak on his behalf, and his family has declined to comment.
Robinson was arrested late on Thursday near St. George, the southern Utah community where he grew up.
Investigators have spoken to Robinson’s relatives and carried out a search warrant at his family’s home in Washington, about 390 kilometres southwest of where the shooting happened.
Kirk, a dominant figure in conservative politics, became a close ally of President Donald Trump after founding the Arizona-based Turning Point USA, one of the nation's largest political organisations.
He brought young, conservative evangelical Christians into politics and his shooting raised fears about increasing political violence in a deeply polarised United States.
While authorities say Robinson hasn’t been cooperating with investigators, they say his family and friends have been talking.
Utah Governor Spencer Cox said at the weekend that those who know Robinson say his politics shifted to the left in recent years and that he spent a lot of time in the “dark corners of the internet.”
Investigators are working on finding a motive for the attack, Cox said, adding that more information may come out once Robinson appears for his initial court hearing.
