Charlie Kirk's alleged assassin is not cooperating with authorities even as he languishes on special watch inside a Utah jail - as President Donald Trump said a lot of people are under 'major investigation' for Kirk's death.

Tyler Robinson, 22, was arrested on Friday in connection with Kirk's shooting death at Utah Valley University earlier in the week.

Authorities have said he confessed to his father, Matt Robinson, that he had been the one to fatally shoot the 31-year-old conservative influencer in the neck.

Matt, who runs a family-owned construction company, then contacted authorities and secured his son before he could be taken into custody.

But Utah Gov. Spencer Cox said on Sunday that the suspect is not cooperating with police as they try to identify a motive for the shocking attack.