New police body camera video shows the final moments of slain NYPD officer Brian Mulkeen — and indicates that cops only opened fire after another cop at the chaotic scene repeatedly warned that the suspect was reaching for a gun.

At that point, six cops began shooting, killing Mulkeen with friendly fire along with the man he was trying to arrest, the video shows.

The body-camera footage recorded by NYPD officer Robert Wichers shows him and Mulkeen pull up to the suspect — later identified as 27-year-old Antonio Williams — in an unmarked police car, along with another cop, near the Edenwald Houses on East 229 Street near Laconia Avenue in the Bronx on Sept. 29 at about 12:25 a.m.

Williams runs off as soon as the cops pull up in front of him, the video shows, and Mulkeen and Wichers sprint after him.

The third cop in their anti-crime squad, identified only as Officer Mahon, remained near the car and detained another suspect who was with Williams. He also radioed for backup.

Mulkeen and Wichers caught up with Williams seconds later on a path near the public housing project and struggled to subdue him, with Mulkeen grappling with him on the pavement, the video shows.

Wichers repeatedly yelled to Mulkeen: “He’s reaching! He’s f—king reaching! He’s reaching for it!” the video shows.

About 30 seconds into the struggle, three other cops responded to the scene — a sergeant, a detective and a police officer — authorities said.

Seconds later, all six cops opened fire at the suspect, firing a total of 15 rounds, police said.

Mulkeen squeezed off five rounds, as did another officer, identified only as Sergeant Valentino, who came to back-up the anti-crime cops. Wichers fired one round; so did Officer Mahon and a “Det. Beddows,” whose first name was also not released.

The other cop who came for back up, an Officer Figueroa, fired two rounds.

Williams and Mulkeen were both killed in the shooting. The cops later found a .32-caliber revolver on Williams that had not been fired.

The NYPD is still investigating the incident and has not determined if any of the cops involved used excessive force.

At a press conference on Friday, Williams’ family blasted the NYPD, saying their “reckless” use of force killed him.

“My brother was killed due to recklessness and unprofessionalism from the NYPD,” his brother, Justin Williams, said. “Two lives were lost and two lives will never be brought back.”

“I saw him standing there waiting for a cab, not bothering anybody,” his father, Shawn Williams, said of the footage.

“NYPD rolls up on him, he runs, they chase, and it ended as we all know … two lives lost unnecessarily.”