WAUKESHA, Wis. — He had been arrested time and again since he was a teenager, accused of battery and domestic abuse and resisting the police. Earlier this month, prosecutors in Milwaukee said, he intentionally ran over a woman he knew with a maroon Ford Escape.
But Darrell E. Brooks, 39, was quickly freed from jail on bond after prosecutors requested what they now say was an inappropriately low bail. By Sunday evening, as a Christmas parade was making its way through downtown Waukesha, Wis., the police were coming for Mr. Brooks again after receiving a report of a domestic dispute involving a knife.
But before Waukesha officers ever reached the site of that dispute, a maroon Ford Escape toppled barriers along the parade route. The police said Mr. Brooks was the driver, and that he sped toward the marching bands and the smiling families and the troupe of “Dancing Grannies” strolling down Main Street, charging on even as he mowed down children and octogenarians. One police officer fired his gun at Mr. Brooks but quickly stopped, Chief Daniel Thompson said, fearful of hitting someone in the crowd.
Five adults died in the vehicle attack and at least 48 people, including children, were injured, some critically. Within minutes, what the mayor described as “a Norman Rockwell type of Christmas parade” in suburban Milwaukee had become a mass casualty incident, with firefighters who were watching the parade with their families suddenly tending to the wounded on the street.
At a hospital not far from the parade route, off-duty doctors rushed to the emergency room on Sunday night. Among the dead were three members of the Milwaukee Dancing Grannies, and the husband of a member of that group.
“That parade became a nightmare,” Mayor Shawn Reilly said Monday as investigators continued to comb through a downtown that parade-goers had fled in such a hurry that they left coolers, strollers and dozens of lawn chairs behind. “Last night, lives were lost during the middle of what should have been a celebration.”
Chief Thompson, of the Waukesha police, said there had been no pursuit by officers before Mr. Brooks steered onto the parade route and no indication that the attack was motivated by terrorism. While the chief said that Mr. Brooks intentionally struck people with the vehicle, he was not able to say whether he drove down the parade route in a rush to escape the earlier confrontation or in a fit of fury.
Mr. Brooks was expected to appear in court on Tuesday afternoon after police referred five counts of first-degree intentional homicide to prosecutors. It was not clear whether he had a lawyer.
Prosecutors in Milwaukee County said they had erred this month in recommending a $1,000 cash bail in the case in which Mr. Brooks was accused, among other things, of running over the woman with his car in the parking lot of a gas station, after which she was hospitalized.
“The state’s bail recommendation in this case was inappropriately low in light of the nature of the recent charges and the pending charges against Mr. Brooks,” the Milwaukee County District Attorney’s Office said in an unsigned statement, which added that an investigation was underway into how that decision was made. It said the bail amount was not “consistent with the risk assessment of the defendant prior to setting of bail.”
John T. Chisholm, the district attorney in Milwaukee, did not immediately respond to an interview request. Mr. Chisholm, a Democrat, is a longtime prosecutor and one of the early proponents of using real case data to address racial disparities in prosecution.
In Waukesha, a usually quiet suburb with about 72,000 residents, people were still coming to terms with the carnage. Public schools were closed, City Hall opened only for a news conference and police cars had cordoned off the parade route during the morning rush hour.
Steve Howard, chief of the Waukesha Fire Department, said every on-duty member of his agency responded to the scene on Sunday, along with several off-duty members who had been lining the streets to watch.
“I’d liken it to a war zone,” Chief Howard said, his voice choked with emotion as he recounted the chaotic scene.
Chief Thompson, of the Police Department, said there was no indication that Mr. Brooks knew anyone attending the parade. He said Mr. Brooks had acted alone and that he was arrested near the parade route.
Mr. Brooks had been in and out of the Wisconsin criminal justice system throughout his adult life, racking up arrests in the Milwaukee area for resisting or obstructing an officer, bail jumping, recklessly endangering safety, disorderly conduct and battery, among other charges.
In rap tracks he posted to a SoundCloud profile, he described himself as growing up in a dangerous Milwaukee neighborhood and having trouble with the legal system. In one video he posted online, he appeared to rap alongside a maroon Ford Escape.
The incident in the gas station parking lot occurred on Nov. 2. The woman injured by the vehicle told the police that Mr. Brooks had punched her in the face in a hotel room, then followed her in his S.U.V. into the parking lot, where he hit her with the car.
“Officers observed tire tracks on her left pants leg,” wrote one of the officers, according to a criminal complaint charging him with recklessly endangering the woman, which carries a possible sentence of 10 years in prison.
The woman was treated for injuries that included facial cuts and bruises. The police observed “swelling on her lip and dried blood on her face.”
Mr. Brooks has a long history of domestic abuse allegations and bench warrants in a paternity case, which are typically issued for nonpayment of child support. In February, a judge in Waukesha County issued a warrant for his arrest after he reneged on a monthly agreement to pay a woman in the area $151 in child support and $50 in money he owed her, in a case that dates back more than a decade.
In many of his brushes with the law, Mr. Brooks was accused of resisting arrest or attempting to obstruct officers, according to the court records. That pattern held true earlier this month: When the police tried to arrest him, he sprinted into his residence and “closed four doors on officers” before they restrained him, according to a criminal complaint.
Marsha Winters, who said she was a friend and occasional lover to Mr. Brooks, said he had stayed with her briefly over the summer after being released from jail. His time lodging in the family’s basement lasted only a day or two in August, she said.
“I’m just in shock,” Ms. Winters said. “I thought I knew him. I guess you don’t know what people are capable of until they do something like this.”
In Waukesha, residents gathered Monday evening for a vigil at a downtown park as others came to pick up items they left while fleeing the destruction. Chris Gresky, 36, came to claim a wagon, filled with candy and other bagged snacks, that he left behind while running away with his wife and children, past bodies strewn on the ground.
“We saw the car, and knew it wasn’t quite right,” Mr. Gresky said. “We watched it get up on the curb and then kind of go on two wheels.”
“This morning,” Mr. Gresky said, “my 6-year-old was asking ‘Why? Why did he do that?’”
Mitch Smith reported from Waukesha, and Dan Simmons from Milwaukee. Brandon Dupré and Ellen Almer Durston contributed reporting from Waukesha. Reporting was also contributed by Ben Decker, Shaila Dewan, Giulia Heyward and Shawn Hubler. Kitty Bennett contributed research.