The assassin who gunned down conservative firebrand Charlie Kirk with a single, precise shot on a Utah campus was almost certainly a trained professional who may take years to catch, a former FBI chief has warned.

Chris Swecker, who served as assistant FBI director in the 2000s, told the Daily Mail that everything about the Wednesday shooting at Utah Valley University suggested a calculated, and methodical operation rather than the chaotic violence America has grown grimly accustomed to.