The unnamed roommate told investigators that Tyler Robinson contacted her after last Wednesday's shooting on the campus of Utah Valley University in Orem to say he had left a confession under his computer keyboard, prosecutors said.
Authorities said the unnamed roommate was a transgender person in the process of transitioning from male to female and was romantically involved with Robinson, who is accused of Kirk's murder.
The BBC has published a full transcript of the correspondence that took place on the day of the shooting, which the roommate handed over to investigators.
Robinson: Stop what you're doing, look under my keyboard.
[There was a note at the indicated location that read:"I had the opportunity to destroy Charlie Kirk, and I will use it."]
Roommate: What??????????????? You are joking, right????
Robinson: I'm still okay, my dear, but I'm stuck in Orem for a little while longer. I'll be home soon, but I still have to get my rifle. Honestly, I was hoping to keep it a secret until I die of old age. I'm sorry I had to involve you in this.