The FBI released a photo of the main suspect in the murder case of Charlie Kirk during a briefing on Thursday.
The FBI also offered a reward of up to $100,000 for information leading to the identification and arrest of the person or people responsible for the shooting.
The FBI is asking the public to assist law enforcement in identifying the suspect.
The shooter has not been publicly identified, but the FBI circulated grainy images apparently taken from security cameras showing a "person of interest" wearing a black top, black sunglasses, and a dark baseball cap. The top appears to have an image of a bald eagle flying across a US flag.
FBI and state officials said the killer arrived on the campus a few minutes before the event began, a debate led by Kirk titled "Prove Me Wrong" outdoors in front of about 3,000 people at Utah Valley University in Orem, Utah, about 40 miles (65 km) south of Salt Lake City.
Videos show suspect going on roof prior to shooting at Kirk
Security-camera videos show a person going up stairwells to get onto a roof before firing at Kirk, the officials told a press conference. Kirk, a staunch defender of gun rights, was answering an audience question about mass shootings when the bullet struck his neck. Audience members fled in panic.
The shooter jumped off the roof and fled into an adjoining neighborhood, Robert Bohls, the FBI special agent in charge, told reporters.
Investigators found a "high-powered, bolt-action" rifle in a nearby wooded area and were examining that along with palm prints and footprints for clues. On Thursday, with classes canceled, the roof of the building on the otherwise deserted campus and the nearby woods were strung with yellow tape as investigators scoured them for evidence.
The shooter appears to be of college age and "blended in well" on the campus, Utah Public Safety Commissioner Beau Mason told reporters.
This is a developing story.