The classification "aggravated murder" means that he may be sentenced to death if he is found guilty.
I intend to plead for the death penalty, says prosecutor Jeff Gray.
Right-wing debater Charlie Kirk was shot dead last week when he spoke in front of a crowd at Utah Valley University in the USA. After an intense hunt, Robinson was arrested on Thursday.
Robinson's DNA has been found on the trigger of the suspected murder weapon, according to Jeff Gray.
In addition to murder, the 22-year-old is accused, among other things, of firearms offenses and of trying to hinder the investigation.
The prosecutor quotes text messages at the press conference that the suspect is said to have written to his roommate in connection with the deed. On one occasion, the roommate is said to have asked Robinson why he did it - shot Charlie Kirk. Robinson replied: "I had had enough of his hate."
Robinson is also said to have left a note under his keyboard that said he planned to murder Kirk.
The text messages also show that the suspect tried to retrieve his rifle, which he had put away during his escape from the crime scene, but that it was not possible due to police presence.
