The bullet that killed conservative commentator Charlie Kirk did not match the rifle used by suspected killer Tyler Robinson, a bombshell new court filing states. Robinson, 22, is facing capital murder charges and a potential death sentence for Kirk's murder at Utah Valley University on September 10. But his defense attorneys now argue that the Bureau of Alcohol, Tobacco, Firearms and Explosives 'was unable to identify the bullet recovered at autopsy to the rifle allegedly tied to Mr Robinson.' The defense team may now offer the ATF firearm analyst's testimony as exculpatory evidence, they said in a motion filed on Friday to push the preliminary hearing back at least six months, Fox News reports.