OREM, United States (AFP)-US authorities investigating the killing of right-wing youth leader Charlie Kirk released pictures Thursday of a man they were hunting, as Donald Trump paid tribute to a “giant of his generation.”

Kirk, a 31-year-old superstar on the Republican right who was credited with helping Trump return to the presidency last year, was shot while addressing a large crowd at Utah Valley University on Wednesday.

The killing — described by the FBI as a “targeted event” — shocked a nation already reeling from political tensions half a year into Trump’s second term.

Authorities acknowledged the gunman remained at large after having escaped initially into woodland.

“We’re doing everything we can to find him, and we’re not sure how far he has gone yet, but we will do our best,” FBI Special Agent Robert Bohls told a media briefing.

Authorities said the suspect was of university age and that they had quality video footage, yet to be released, identifying the man. The FBI also announced a reward of up to $100,000 for information.

The FBI issued grainy photos of a person of interest — not yet a suspect — and asked for the public’s help identifying him. The pictures showed a man wearing a black baseball cap, dark sunglasses, and what appeared to be jeans, with a long-sleeved top emblazoned with a design including an American flag.

Bohls said the presumed murder weapon had been found.

“It is a high powered bolt action rifle. That rifle was recovered in a wooded area where the shooter had fled,” the FBI agent said.