articleAuthorities said the gun used in the killing of Charlie Kirk may be a decades-old, untraceable rifle. Authorities said the firearm belonged to the grandfather of Tyler Robinson, the 22-year-old Utah man accused of assassinating Kirk . Police allege Robinson may have deliberately chosen the rifle because it was difficult to trace. "I’m worried what my old man would do if I don’t bring back grandpa’s rifle," Robinson wrote, according to the New York Post . Booking photos for Tyler Robinson, 22, the suspect in the Utah assassination of Turning Point USA founder Charlie Kirk.