DNA found at the scene of the murder of US conservative influencer Charlie Kirk has been matched to suspect Tyler Robinson, FBI director Kash Patel said on Monday.

Robinson, 22, was arrested last Thursday after a 33-hour manhunt and is expected to be formally charged in the murder later this week. Authorities said the suspect used a sniper rifle to shoot Kirk with a single bullet to the neck from a rooftop.

"I can report today that the DNA hits from the towel that was wrapped around the firearm and the DNA on the screwdriver are positively processed for the suspect in custody," Patel said on Fox News on Monday morning, referring to a screwdriver recovered from the scene.

Patel also discussed a note that Robinson is believed to have written before the crime.

The note is "basically saying... 'I have the opportunity to take out Charlie Kirk', and I'm going to take it that note was written before the shooting," Patel said.

He added that note was left at the suspect's family home.

"Even though it has been destroyed, we have found forensic evidence of the note," the FBI director said.

Kirk, a close ally of US President Donald Trump, was shot last Wednesday during a speaking event on a Utah university campus. He was the founder of the conservative youth political group Turning Point USA.

The father-of-two used his audiences on TikTok, Instagram and YouTube to build support for conservative talking points and spread carefully edited clips of his interactions during debates at his many college events. (AFP)