Opening arguments began Monday in the case of an NYPD officer who is accused of shooting and killing a man last year in Brooklyn.

Officer Wayne Isaacs is charged with second-degree murder and manslaughter in the death of 37-year-old Delrawn Small, who was shot and killed on July 4 of last year in Cypress Hills.

Investigators say Small and Isaacs got into a fight at a red light on Atlantic Avenue.

Isaacs was off-duty at the time. He said Small got out of his car and punched him in the face through his car window.

But surveillance video shows that Small was immediately shot as he approached the car.

This is the first case to be tried under an executive order by the governor that gives the attorney general's office — rather than the local district attorney — the power to investigate and prosecute officers for civilian shootings.

Wiping away tears, Small's sister had to leave the courtroom as the prosecutor and defense talked about the condition of her brother's bullet-riddled body.

"Very difficult and emotional," Small's widow, Wenona Small, said with supporters. "I'm going to try hold myself together as best as I can." 

Defense lawyers said Issacs acted in self-defense after the 6 feet, 1 inch-tall, 237-pound victim walked up to the off-duty officer's car at a red light and punched him in the face.

"Nothing good comes of these road rage incidents," Defense Attorney Stephen Worth said. "He is a police officer, he was entitled to have the weapon, he was entitled to defend himself and, under the circumstance of this case, he was entitled to use the weapon, and he did."

"Sadly, Mr. Small was dead. It was of his own doing," Worth said.

In opening statements, prosecutors pointed to the surveillance videos from the area. They said as soon as Small approached the officer's car, Issacs fired three shots in a blink of an eye, killing the 37-year-old.

"He was not entitled to take Delrawn's life," said Victoria Davis, Small's sister. "Delrawn had the right to live. Delrawn was an unarmed man who was killed unjustly."

"What he is saying here to this jury is that it is ok to kill an unarmed man for striking someone in the face, and that is disgusting," said Hawk Newsome, a member of Black Lives Matter Of NY. "No one would make that argument if it was any other situation than a black man being shot by a police officer."

Defense lawyers said say they have not decided yet if Isaacs will take the stand in his own defense.