It was later confirmed that the father-of-two had died, at the age of 31, and a manhunt for his killer is underway.
Footage has been shared on social media appearing to show a person clad in black lying down on the roof of a nearby building, before jumping up and running away.
The weapon has since been recovered, a .30 caliber hunting rifle, and a law enforcement bulletin reportedly reveals the bullets had messaging on them.
The Wall Street Journal quotes a source as saying the ammunition was engraved with ‘messages of transgender and antifascist ideology.’
According to the Daily Mail, a source claims the rifle was discovered wrapped up in a towel, with a spent cartridge in the chamber.
A magazine was also found containing three unspent rounds, all of which had wording written on them.
Robert Bohls is a special agent in charge of Salt Lake City field office for the FBI, and he said the ‘high-powered bolt action rifle’ was found in a wooded area.
He said the shooter is believed to be male and of college age, and is thought to have fled to the woods after the killing.
The rifle has now been sent to an FBI lab for further analysis, and palm and footwear prints were also discovered on the scene.
More than 130 tips have been received about potential suspects, who the first-responders on the scene described as being dressed all in black with aviator-style sunglasses.
Beau Mason, Utah’s public safety chief, added that they have ‘good video footage’ of the suspect.
Kirk was speaking to students at the university, and had answered questions about transgender individuals who had been involved in mass shootings moments before he was assassinated, after answering a question about gun violence.
He was asked: “Do you know how many transgender Americans have been mass shooters over the last 10 years?” and Kirk replied: “Too many.”
They then asked: “Do you know how many mass shooters there have been in America over the last 10 years?” to which Kirk answered, “Counting or not counting gang violence?” and he was shot seconds later.
The search for his killer continues.