Patel said the suspect Tyler Robinson texted and wrote a piece of paper saying he had an opportunity to overthrow Charlie Kirk before planning to fire.
Patel said the document had been revoked, but investigators had collected forensic evidence to prove its existence and confirmed the content through interviews.
Patel did not specify who received the text messages or whether anyone had seen the handwritten piece before the attack, while investigators have not yet released a motive.
Law enforcement officials believe that Robinson acted alone in the assassination of Kirk, but they are still investigating whether anyone else was involved in the assassination plan.
According to an expert, Robinson sent a message via the online platform Discord to friends, seemingly confessing to his crime on the evening of September 12 (local time) right before his arrest.
That was me at UVU ( Utah Valley University) yesterday. I apologize for all this" - the message from the account belonged to Robinson wrote, according to the source quoting the two people familiar with the conversation as well as the screenshots they collected.
Charlie Kirk - an influential ally of US President Donald Trump, co-founder of the leading conservative student organization Turning Point USA - was assassinated with a single rifle, on September 10 at an event at Valley Utah State University in Orem, about 65km south of Salt Lake City.
