A 71-year-old man who was briefly detained moments after the assassination of Charlie Kirk tried to help the suspected gunman escape by faking a confession, authorities say.

Utah County Sheriff Michael Smith said George Zinn admitted to police that he had "yelled that he was the shooter to allow the actual suspect to flee".

The prime suspect in the killing is 22-year-old Tyler Robinson, who appeared to acknowledge Mr Zinn's initial arrest after the shooting, texting his roommate that the police had "grabbed some crazy old dude".

Mr Zinn is being held on obstruction of justice charges. Separately, he has also been charged with possession of child sex abuse material.

George Zinn was one of two people that the police had detained for questioning after conservative commentator Charlie Kirk was fatally shot at Utah Valley University on 10 September.