CHICAGO (Reuters) - The white police officer who shot to death a black teen in 2014 fired 16 shots without justification, prosecutors told a Chicago jury on Monday, as the trial began in a decisive case for race relations and policing in the United States’ third-largest city.

FILE PHOTO: Chicago police Officer Jason Van Dyke stands and walks toward the judge's bench at the start of the trial for the killing of Laquan McDonald at the Leighton Criminal Court Building in Chicago, Illinois, U.S., September 14, 2018. Antonio Perez/Pool/Chicago Tribune via REUTERS/File Photo

“What he saw that night was a black boy with the audacity to ignore the police,” special prosecutor Joseph McMahon said during his opening statement of the officer, Jason Van Dyke. “Not a single shot was necessary.”

Van Dyke’s defense lawyer, Daniel Herbert, portrayed 17-year-old Laquan McDonald as a dangerous drug user who caused the officer to fear for his safety.

“McDonald was an out-of-control criminal running with a knife,” Herbert told jurors. “What happened to Laquan McDonald is a tragedy. It’s a tragedy, not a murder.”

The deaths of mostly unarmed black men at the hands of police officers across the United States in recent years have led to protests and sometimes violence in major U.S. cities. The killings helped give rise to the Black Lives Matter movement and became an issue in the 2016 U.S. presidential campaign.

Eight witnesses for the prosecution, including a dispatcher, a Federal Bureau of Investigation forensic examiner and Chicago police officers took the stand on Monday.

Officer Joseph McElligott, who responded to the incident before the shooting, said McDonald swiped a knife at his squad car and kept walking, ignoring at least 30 orders to drop his weapon. Asked by prosecutors why he did not shoot McDonald, McElligott, who had followed McDonald on foot with his gun drawn, said McDonald did not move directly toward him and he was trying to buy time for a Taser to arrive.

Prosecutors were expected to continue to call witnesses on Tuesday.

Prosecutors showed jurors a soundless dashboard camera video that showed Van Dyke gunning down McDonald as he appeared to move away from officers. The video’s public release in 2015 spurred protests, fed a national debate over the use of excessive force by police against minorities and led to the ousting of local officials.

The video, released by the city more than a year after the shooting in response to a Freedom Of Information Act lawsuit, sparked days of protests in Chicago. Chicago Police Superintendent Garry McCarthy, who has announced a mayoral run, was fired, and activists called for the resignation of Chicago Mayor Rahm Emanuel.

Emanuel said on Sept. 4 he would not seek a third term after facing widespread criticism over his handling of the city’s gun violence. He did not specifically cite McDonald in his announcement.

A U.S. Department of Justice investigation that began after the video’s release found Chicago police routinely violated people’s civil rights, citing excessive force and racially discriminatory conduct.

Van Dyke, now 40, opted for a jury trial on Friday following the selection of a 12-person jury and five alternate jurors. He was suspended without pay after he was first charged in 2015.

The 12-person jury includes one black person.

Van Dyke’s attorneys on Monday morning asked Cook County Judge Vincent Gaughan to dismiss the jurors, saying “the negative and inflammatory rhetoric” surrounding the case had made it impossible for them to be impartial, but the judge rejected that argument. Gaughan also denied a defense motion to move the trial out of Chicago.

Van Dyke faces first-degree murder, aggravated battery and official misconduct charges. He is the first Chicago police officer to face a murder charge for an on-duty incident in decades.

Three Chicago Police Department officers were indicted in June 2017 for conspiring to cover up McDonald’s shooting. They have not yet been tried.