In opening statements in the murder trial of New York City police Officer Wayne Isaacs, who’s accused of shooting and killing unarmed civilian Delrawn Small, a prosecutor from the New York Attorney General’s Office said Monday that the officer initiated the fatal encounter by cutting Small off in traffic.

But an attorney for Isaacs, the first police officer to be prosecuted by the state attorney general for killing an unarmed civilian since the office was given the authority to investigate such cases in 2015, argued Small was the aggressor and that Isaacs fired the three rounds that took Small’s life in self-defense.

The trial for Isaacs, who’s charged with second-degree murder and first-degree manslaughter, presents an initial test for the Special Investigations and Prosecutions Unit created within the Attorney General’s Office to handle police shootings.

Isaacs was off-duty and in plainclothes in the early morning hours of July 4, 2016, following his shift with the 79th Precinct in the Bedford-Stuyvesant section of Brooklyn.

Isaacs first encountered Small at the intersection of Atlantic Avenue and Bradford Street in the Cypress Hills neighborhood in Brooklyn, where Assistant Attorney General Jose Nieves said Isaacs cut Small off in traffic.

Small became upset over the incident, Nieves said, and approached Isaacs’ vehicle. Isaacs acted quickly, firing three rounds into Small, the prosecutor said, then “strolled” past Small and called 911 to report that Small assaulted him.

“At the end of this case, the evidence will show that the defendant shot and killed Delrawn Small and that he had no legal justification to do so,” Nieves said.

Nieves also said Isaacs neglected to identify himself as a police officer before he shot Small, which drew an objection from defense attorney Stephen Worth. Brooklyn Criminal Court Judge Alexander Jeong overruled.

Assistant Attorney General Joshua Gradinger is also prosecuting the case.

During opening arguments from the defense, Worth, a partner at Worth, Longworth & London, argued Small was legally drunk from a Fourth of July party he attended before the altercation with Isaacs—a contention that drew an objection from the prosecution that Jeong overruled—and that there was no “road rage” incident prior to the shooting.

Worth also noted that Small’s girlfriend described him as someone who gets “so angry, so fast” and that Small crossed two lanes of traffic to confront Isaacs.

“He’s a menace, he’s angry, he’s intoxicated and he in fact assaults Mr. Isaacs,” Worth said. Isaacs is also represented by Michael Martinez of Worth Longworth.

On Monday, jurors also heard testimony from a New York City detective who investigated the scene, Isaacs’ supervisor and an emergency medical technician who responded.

During the testimony of the EMT, Catherine Renta, jurors were shown a black-and-white photo of Small’s body while lying on the pavement, at which point members of Small’s family were visibly shaken.

Nieves told jurors that the evidence presented in the trial will include video footage of the shooting captured from a nearby surveillance camera. Video of the shooting was publicly released last year.

In July 2015, in the midst of a public outcry over police killings of unarmed civilians, Gov. Andrew Cuomo signed an executive order giving prosecutorial powers to the New York Attorney General for cases in which an officer caused the death of an unarmed civilian.

Among the cases that stoked public ire was the July 2014 death of Eric Garner, who New York City police Officer Daniel Pantaleo placed in a fatal chokehold. A grand jury on Staten Island declined to indict Pantaleo for Garner’s death.

Isaacs is the only officer to be charged so far, while other incidents are still under investigation.

“Our Special Investigations and Prosecutions Unit is committed to following the facts wherever they may lead, without fear or favor,” said Amy Spitalnick, a spokeswoman for New York Attorney General Eric Schneiderman’s office, said in an email. “We look forward to proving our case in court.”