WASHINGTON 

The FBI on Thursday released two photos of a "person of interest" in the fatal shooting of American right-wing commentator Charlie Kirk, appealing to the public for assistance in identifying the individual.

The grainy photos appear to depict a college-age male clad in a black long-sleeve t-shirt, jeans, a baseball cap and black sunglasses.

Kirk, 31, was fatally shot Wednesday afternoon while addressing a group of students at Utah Valley University in the city of Orem, some 40 miles (64.4 kilometers) south of Salt Lake City. The apparent targeted attack occurred despite security, including six university police officers and Kirk's private team.  

Online videos captured the moment a bullet struck Kirk as he spoke, sending students fleeing in panic. He was rushed to a hospital where he was pronounced dead hours later.

Earlier Thursday, the FBI said investigators found a "high-powered bolt-action rifle" that was recovered in a wooded area linked to the suspected shooter's escape route.

Multiple media reports suggested that ammunition engraved with "transgender and antifascist ideology" was found in the rifle. The reports cited an internal law enforcement document.

The New York Times cited an anonymous senior law enforcement official who stressed that the information had not been verified, did not match other summaries of evidence and may have been misread.

The investigation has so far been able to track the suspect's movements starting roughly 30 minutes before Kirk was shot, Utah Department of Public Safety Commissioner Beau Mason said during a news conference. Authorities believe the suspect arrived near the Utah Valley University campus at 11.52 am local time (1752GMT), and made his way to the roof and to what Robert Bohls, the FBI special agent in charge of the Salt Lake City field office, described as a "shooting location."

After the shooting, the suspect moved to the other side of the building, jumped down and made his way into a nearby neighborhood where investigators have sought home camera surveillance footage.

Two people of interest were taken into custody in the aftermath of the shooting, but were later released after being cleared of suspicion. Mason said both individuals faced "threats" after being released, and asked the public to be "patient with the investigative process."

"These individuals were not suspects. They were people of interest. We asked that you do not impose into those people and that investigative process. They don't deserve that harassment," said Mason.