Six people were killed and 62 injured in the chaos that unfolded in Waukesha, Wisconsin, which is about 20 miles west of downtown Milwaukee.
Prosecutors announced during the hearing that there was a sixth victim, a child, and that they planned on filing an additional count of intentional homicide later this week.
If convicted Mr Brooks, 39, would face a mandatory life sentence in prison.
The sixth victim has now been named on a GoFundMe page as Jackson Sparks, aged eight.
Both he and his brother Tucker, 12, were injured when the SUV driven by Brooks entered the parade route.
Jackson underwent brain surgery on Sunday evening but succumbed to his injuries and passed away on Tuesday afternoon.
Crowds were gathered along Main Street for the parade when a red SUV drove through a series of barricades and mowed through the parade route on Sunday afternoon.
Prosecutors are expected to file other lesser charges in relation to those people injured in the attack.
Newly filed court documents quote a witness to the incident who told investigators, “As I continued to watch the SUV, it continued to drive in a zig zag motion. It was like the SUV was trying to avoid vehicles, not people. There was no attempt made by the vehicle to stop, much less slow down.”
The criminal complaint does not give any details about the actual arrest or if Mr Brooks made any statements to police.
Before the hearing Court Commissioner Kevin Costello warned people in the courtroom to remain calm despite the allegations against Mr Brooks and to leave if they were overcome with emotion.
The defendant appeared to be wearing a protective vest as he was led into court to sit beside his lawyers, and prosectors asked for $5m cash bail saying “it is warranted given his history” and described him as “a threat to our community.”
Commissioner Costello said that he believed Mr Brooks was a flight risk and that he didn’t “do well under pressure.”
“You don’t respond well to common sense within our community, our society,” he said as he set bail at $5m
“I am an old guy who has been doing this for almost 40 years. The nature of this offence is shocking, the detail of which I was not expecting here today,” said Commissioner Costello.
“Two detectives not only tried to stop this, but rendered an opinion that this was an intentional act.
“You are presumed innocent sir, but that is what the allegations are. I have not seen anything like this in my entire career and it seems like a very strong case for the state.
“The bail is extraordinarily high but it is an extraordinarily big case and there is an extraordinary history of this gentleman hurting people and not following court orders, not following criminal laws or societal norms.”
The five deceased victims already identified are Virginia Sorenson, 79; LeAnna Owen, 71; Tamara Durand, 52; Jane Kulich, 52; and Wilhelm Hospel, 81.
The injured included a Catholic priest and members of the Milwaukee Dancing Grannies group.
Mr Brooks was arrested earlier this month for using a 2010 maroon Ford Escape to run over the mother of his child, according to court documents.
A criminal complaint in that incident states that a woman told police that Mr Brooks had pulled up beside her following an earlier domestic dispute.
He told her to get into his car, and when she refused he allegedly hit her in the face with a closed fist, according to the complaint.
He was released on a $1,000 bond on charges that included domestic abuse and was accused of using a car to cause injury, according to a criminal complaint.
Mr Brooks is also a registered sex offender in Nevada, where he was convicted in 2006 of impregnating a 15-year-old, according to ABC News.
He was then arrested again in 2016 when he failed to obey sex offender laws.
He bailed out on the charge but never returned to court, according to police in Sparks, Nevada and a warrant was issued in August 2016 for that failure to appear.
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