Kirk, 31, was speaking at an outdoor campus gathering shortly after noon when he was shot.
The FBI later said the suspected gunman had positioned himself on the rooftop of a nearby building overlooking the event area. Kirk was transported to a local hospital, where he was pronounced dead.
The attack transformed the university campus into a crime scene as students, event attendees and witnesses fled or sought shelter while law enforcement officers secured the area. Investigators quickly began collecting evidence and working to reconstruct the events leading up to the shooting.
Federal and local authorities launched an extensive search for the suspect. According to investigators, a high-powered bolt-action rifle believed to have been used in the shooting was recovered from a wooded area where the gunman was believed to have fled.
Authorities also collected forensic evidence from the rooftop, including footwear impressions, a palm print and forearm impressions. The FBI appealed to the public for photographs, videos and other information that could help investigators identify the person responsible.
The bureau announced a reward of up to $100,000 for information leading to the identification and arrest of those responsible.