Tyler Robinson, the 22-year-old Utah man accused of assassinating conservative activist Charlie Kirk, has been charged with aggravated murder, a US prosecutor announced, saying Robinson left behind his DNA on the trigger of the rifle that fired the fatal shot.

The charge means Robinson could face the death penalty if convicted of killing Kirk last week at Utah Valley University in Orem, about 64km south of Salt Lake City.

“The murder of Charlie Kirk is an American tragedy,” Utah County Attorney Jeff Gray said in announcing the charges.

Kirk was gunned down on September 10 as he spoke with students 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 discarded the rifle and clothing and asked 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 also was 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 Tuesday afternoon.

It was unclear whether Robinson had an attorney who could speak on his behalf, and his family has declined to comment to The Associated Press.

Robinson appears to have stayed in the area after shooting Kirk and ditching his rifle, authorities said.

Text messages shared with a roommate

In a text exchange with his roommate released by authorities, Robinson wrote, “I had planned to grab my rifle from my drop point shortly after, but most of that side of town got locked down. Its quiet, almost enough to get out, but theres one vehicle lingering.”

Then he wrote: “Going to attempt to retrieve it again, hopefully they have moved on. I haven’t seen anything about them finding it.”

And after that, he sent: “I can get close to it but there is a squad car parked right by it. I think they already swept that spot, but I don’t wanna chance it.”

The texts shared in court documents do not have timestamps, and it’s unclear how long after the shooting Robinson was texting.

Robinson was arrested late 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, Utah, about 390km southwest of where the shooting happened.

Kirk, a dominant figure in conservative politics, became a confidant of President Donald Trump after founding Arizona-based Turning Point USA, one of the nation’s largest political organisations.

He brought young, conservative evangelical Christians into politics. His shooting raised fears about increasing political violence in a deeply polarised US.

While authorities say Robinson hasn’t been cooperating with investigators, they say his family and friends have been talking.

Utah Governor Spencer Cox said over the weekend that those who know Robinson say his politics shifted left in recent years and he spent a lot of time in the “dark corners of the internet.”

FBI Director Kash Patel said agents were looking at “anyone and everyone” who was involved in a gaming chatroom on the social media platform Discord with Robinson. The chatroom involved “a lot more” than 20 people, Patel said Tuesday during a Senate Judiciary Committee hearing in Washington.

“We are investigating Charlie’s assassination fully and completely and running out every lead related to any allegation of broader violence,” Patel said in response to a question about whether the Kirk shooting was being treated as part of a broader trend of violence against religious groups.

Investigators are working on finding a motive for the attack, Utah’s governor said Sunday, adding that more information may come out once Robinson appears for his initial court hearing.

Cox said Robinson’s romantic partner was transgender, which some politicians have pointed to as a sign the suspect was targeting Kirk for his anti-transgender views. But authorities have not said whether that played a role.

Kirk was shot while taking a question that touched on mass shootings, gun violence and transgender people.

Gray declined to answer a question about whether transgender issues played a role in the motive behind Kirk’s shooting.

He pointed to the charging documents, saying they summed up those points.

The charges against Robinson

The charges filed Tuesday carry two enhancements including committing several of the crimes in front of or close to children and carrying out violence based on the subject’s political beliefs.

Gray declined to say whether Robinson’s roommate could face charges or whether anyone else might face charges. He also declined to say whether Robinson was cooperating or whether his parents or roommate had continued to cooperate.

In the days since Kirk’s assassination, Americans have found themselves facing questions about rising political violence, the deep divisions that brought the nation here and whether anything can change.

Despite calls for greater civility, some who opposed Kirk’s provocative statements about gender, race and politics criticised him after his death.

Many Republicans have led the push to punish anyone they believe dishonoured him, causing both public and private workers to lose their jobs or face other consequences at work.