New details emerge over bullet used to kill Charlie Kirk in case against suspect Tyler Robinson

More details have been unsealed from the investigation into the death of Charlie Kirk regarding the bullet that killed him and the gun it was allegedly fired from.

The Turning Point USA founder was shot dead on 10 September last year at Utah Valley University, a man named Tyler Robinson was later arrested and charged with the killing.

Prosecutors allege that he carried out the attack, but Robinson's defence have argued that the bullet which killed Kirk may not have matched up to a rifle connected with the defendant, a .30-06 calibre Mauser model 98.

In a court filing the defence argued that the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) had been 'unable to identify the bullet recovered at autopsy to the rifle allegedly tied to Mr Robinson'.

According to the Daily Mail, a recently unsealed filing included the details that among the evidence investigated in lab was a .30-06 calibre cartridge case that had been 'identified as having been fired in the Exhibit 1 rifle', which is a .30-06 calibre Mauser model 98.

Unsealed court documents have said it's 'inconclusive' whether a bullet fragment recovered was fired from the gun allegedly used to kill Charlie Kirk (Andrew Harnik/Getty Images)

Three other unfired cartridges of the same calibre were also examined.

Also in the investigation was that a '.30-caliber class deformed/damaged bullet jacket fragment' was recovered during the autopsy, but that it 'could not be identified or excluded' as having been fired from a rifle linked to Robinson.

Investigators findings in this regard were 'inconclusive', as they noted that markings on the bullet jacket fragment from the gun's rifling had characteristics consistent with 'numerous makes and models' of the gun.

To sum up, the cartridge casing has been identified as fired from the rifle but investigators could not conclude whether the deformed bullet jacket fragment recovered had been fired from such a weapon or not.

When a bullet is fired from a gun there will be marks made on it which can help investigators determine what kind of barrel the bullet came from, but in this case the markings are inconclusive in determining what make and model of weapon fired it.

Investigators connected a cartridge casing with the weapon, court documents show (Bethany Baker-Pool/Getty Images)

Ballistics experts have said it's not uncommon for bullets fired, especially from rifles, not to be matched to a firearm.

Steven Howard told the Daily Mail: "It's pretty common with rifles, not so much with handguns, but it happens also with them.

"Rifles have so much velocity and therefore so much energy, that the bullets a lot of times damage themselves to the point that you can't realistically match them up because they're so damaged."

He noted that 'ballistics comparison is just one part' of the investigation.

Prosecutors are claiming Robinson's DNA was found on the trigger of the rifle, the fired cartridge casing, and two unfired cartridges.

Robinson is due in court today (17 April) for a debate over whether cameras will be allowed into the courtroom for his trial, while a preliminary hearing has been scheduled for 17 May.