On videos spread on social media, it can be seen how Kirk, after a shot is heard, collapses at the same time as blood gushes from his neck.
About an hour later, President Donald Trump, who was close to Kirk, announced that the 31-year-old was dead.
The shot was fired by a lone perpetrator from a roof about 130 meters away, according to the authorities. After firing the shot, he jumped down from the building and ran from the scene to a forest area, where the suspected murder weapon, a repeating rifle, was later found.
This was followed by an intense hunt with both local and federal police involved, and the authorities soon released grainy surveillance images of the suspected shooter.
Many tips from the public
In the initial stage, two people were arrested, both of whom were released when the suspicions against them could be quickly dismissed.
Tips from the public continued to pour in to the police, and on Friday, FBI chief Kash Patel said they had received over 11,000 tips.
And on the same day, the news came, via Donald Trump in Fox & Friends morning sofa, that they had "with the greatest likelihood" arrested the perpetrator.
At a press conference, Utah Governor Spencer Cox confirmed that they had arrested 22-year-old Tyler Robinson as a suspect in the murder.
Relatives helped the police
The arrest could be made after a family member of Robinson contacted a friend, who in turn contacted the authorities with the information that Robinson had confessed or at least hinted at his involvement in the murder.
According to sources to the news agency AP, Robinson's father recognized him in the surveillance images released and then urged him to surrender to the police. The father is said to have asked a youth pastor for help in convincing his son to do so, according to the source.
During the investigation, Robinson's family members have stated that he had recently become increasingly politically engaged. Robinson is also said to have spoken critically of Kirk and mentioned that the right-wing debater would soon be attending an event in Utah.
Without a previous record
The suspected 22-year-old is registered at his parents' home in St. George in southern Utah, about 40 miles southwest of Utah Valley University.
He does not seem to have been known to the police before, writes AP.
On surveillance footage, it can be seen how Robinson arrives at the university area on Wednesday morning, nearly four hours before the fatal shooting, according to Cox. He also stated that the authorities had spoken to a roommate of Robinson who had shown them a social media conversation with a user named "Tyler". In the messages, a rifle left in a green area was mentioned.
It was in a forest area that the suspected murder weapon was found after the shooting. On rifle shells that had not been fired, several engraved messages were found, including "Hi fascist! Take this!", according to Cox.
Formal charges against Robinson are expected to be brought on Tuesday, when he makes his first court appearance.
