WASHINGTON 

Investigators are "making big progress" as they seek to identify and apprehend a suspect in the fatal shooting of American conservative commentator Charlie Kirk, President Donald Trump said Thursday.

"I hear they're making big progress, and we'll have to see what happens," Trump said as he departed the White House. "Progress is being made. He's an animal, a total animal. And hopefully they'll have him, and they'll get him. What he did is disgraceful."

Trump said he would like his supporters to respond to the killing nonviolently, saying Kirk "was an advocate of non-violence." Asked if he has an indication of the motive behind the shooting, he said: "I have an indication, yeah, but we'll let you know about that later."

No suspect has yet been taken into custody -- more than 24 hours after Kirk was fatally shot at Utah Valley University on Wednesday afternoon.

The Utah Department of Public Safety said in a statement issued late Thursday afternoon that "multiple leads are currently being investigated." An earlier press conference was abruptly cancelled due to what law enforcement called "rapid developments in our investigation," and it is unclear if officials will hold another briefing Thursday.

Earlier Thursday, the FBI offered a reward of up to $100,000 for information leading to the arrest of the person who fatally shot Kirk.

The bureau separately released a pair of photos of a "person of interest" in the fatal shooting of the American right-wing commentator, 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 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.

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 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 ask that you do not impose into those people and that investigative process. They don't deserve that harassment," said Mason.