KENOSHA, Wis. — On the first day of testimony in the homicide trial of Kyle Rittenhouse, prosecutors and defense lawyers offered sharply divergent portrayals of Mr. Rittenhouse, an 18-year-old from Illinois who faces the prospect of life in prison.
Prosecutors began their case by describing Mr. Rittenhouse as a dangerous type of tourist, a teenager who came to Kenosha, Wis., bearing a military-style semiautomatic rifle that he possessed illegally, bought for him by a friend because he was only 17 at the time. Once he was in a city not his own, said Thomas Binger, an assistant district attorney, Mr. Rittenhouse chased and confronted Joseph Rosenbaum, 36, before fatally shooting him. He then fatally shot Anthony Huber, 26, and wounded Gaige Grosskreutz, who was then 26.
Downtown Kenosha was filled with people who were “drawn to the chaos” of the civil unrest, Mr. Binger said. But, he said, “The evidence will show that hundreds of people were out in the street experiencing chaos and violence. And the only person who killed anyone was the defendant, Kyle Rittenhouse.”
Mark Richards, a defense lawyer for Mr. Rittenhouse, told the jury there was no disputing who fired the fatal shots that night. “It isn’t a whodunit,” he said.
Mr. Richards presented Mr. Rittenhouse as an innocent: a teenager with family and friends in Kenosha who went downtown to scrub graffiti off a school and, later that evening, to help protect vulnerable businesses from damage by rioters. It was then that he was pursued by attackers, Mr. Richards argued, and responded in self-defense.
“Kyle Rittenhouse protected himself,” Mr. Richards said.
The trial is unfolding at the Kenosha County Courthouse, a building that stood heavily barricaded more than 14 months ago during several days of civil unrest following the police shooting of Jacob Blake, who was shot seven times as officers tried to arrest him. This week, downtown Kenosha has been eerily quiet, with few protesters in front of the courthouse and residents avoiding the area as they anxiously wait for the trial to proceed.
Mr. Rittenhouse, who wore a gray suit and maroon shirt and tie, watched the testimony on Tuesday while yawning frequently, whispering with his lawyers and fidgeting with a water bottle. His mother, Wendy, sat behind him, looking stricken and occasionally weeping.
Prosecutors began their case with a description of the events of the night of Aug. 25, 2020, when Mr. Rittenhouse joined a friend, Dominick Black, to head downtown with their rifles.
Mr. Binger, the prosecutor, largely focused on the first shooting that took place, of Mr. Rosenbaum, who was captured on video chasing Mr. Rittenhouse into a parking lot moments before shots were fired. Mr. Binger said the evidence would show that the fatal shot hit Mr. Rosenbaum in the back after he fell forward following shots to his pelvis and leg.
The prosecutor also said infrared video taken from an airplane by the F.B.I. would show that Mr. Rittenhouse had chased Mr. Rosenbaum that evening. The prosecutor noted, too, that Mr. Rittenhouse was carrying a medical kit, but fled after shooting Mr. Rosenbaum while others tried to offer emergency assistance.
Mr. Rittenhouse then ran down Sheridan Road while being chased by other people in the crowd, falling down before firing more shots at close range, killing Mr. Huber and injuring Mr. Grosskreutz.
“They clearly believe he’s an active shooter,” Mr. Binger said, “and they try to stop him.”
In his opening statement, Mr. Richards, the defense lawyer, argued that Mr. Rittenhouse was no stranger to Kenosha even though he lived in Illinois — a point that has been damaging to Mr. Rittenhouse in the eyes of Kenosha residents who question why he came to their community at all.
“The evidence will show that Kyle Rittenhouse had strong ties to Kenosha,” Mr. Richards told the jurors.
Several jurors listened with grim expressions during opening statements, some frowning and keeping their arms folded firmly across their chests. Others leaned forward, furrowing their brows as they listened to the lawyers and watched video and photo exhibits.
The jury was chosen on Monday evening in just a day, resulting in a 20-juror panel of 11 women and nine men.
Mr. Rittenhouse has been charged with six criminal counts, including first-degree reckless homicide, first-degree intentional homicide and attempted first-degree intentional homicide.
Among the three witnesses whom prosecutors called to testify on Tuesday was Mr. Black, the friend who bought the gun for Mr. Rittenhouse during a trip to Ladysmith, Wis., several months before the Kenosha shootings.
Mr. Black, now 20, acknowledged that he was cooperating with prosecutors in hopes of avoiding prison himself. Mr. Black faces two felony counts of giving the gun to Mr. Rittenhouse, who was 17 at the time and too young to buy it under Wisconsin law.
Mr. Black testified that he had dated Mr. Rittenhouse’s sister and that he and Mr. Rittenhouse were once so close that they considered each other brothers.
On the day of the shootings, Mr. Black testified that he and Mr. Rittenhouse went together to downtown Kenosha — with Mr. Black toting his own, nearly identical gun — where they eventually joined other men guarding a set of used car lots.
Mr. Black testified that he stayed on the roof of a building at one of the car lots because he thought it would be safer than mixing with agitated crowds that included people lighting fires and throwing rocks. During questioning by Mr. Richards, the defense lawyer, Mr. Black said that someone from their group told Mr. Rittenhouse to go protect the lot where he eventually shot Mr. Rosenbaum.
Mr. Richards also asked Mr. Black if he had ever tried to stop his younger friend from going downtown with a gun.
“I didn’t say anything,” Mr. Black said.
