The 21-year-old man who was arrested on suspicion of the massacre was on Tuesday notified of suspicion of seven cases of murder. Prosecutor Eric Rinehart states that more criminal classifications will be added.
More than 30 people were injured in the attack.
If convicted, the man will face life in prison without the possibility of parole, according to the prosecutor.
More than 70 shots were fired when a perpetrator opened fire on the parade from a roof in Highland Park. According to the police, he used a semi-automatic rifle of the type AR-15, which has become notorious for use in mass shootings.
The suspect was arrested a few hours later. The motive is unclear, but the police state that he acted alone and that there is no indication of a religious or racist connection.
The man is described as quiet and introverted. But on the internet he showed another page. Among other things, he recorded music and videos with violence and references to other mass murders.