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 attempting to hinder the investigation. In total, he is suspected of seven points.
The prosecutor quotes text messages that the suspect is said to have written to his roommate in connection with the deed at the press conference. 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."
In response to a question from the roommate about how long he had planned the murder, he replied "a little over a week, I think". He urged the roommate to delete the conversation.
Robinson, who on Tuesday made a brief appearance in court via link, is also said to have left a note under his keyboard that said he "had the chance to" murder Kirk and that he thought "take it".
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.
In court, he only said his name and nodded when the prosecutor explained that he would remain in custody without bail.
