Three reputed Brooklyn gang members have been indicted on murder and other charges in last summer’s Crown Heights shooting death of an aide to Gov. Andrew M. Cuomo — a bystander gunned down, authorities said Wednesday — after a crowded street festival became “a killing field.”

Micah Alleyne, 24 of Jamaica, Queens, Tyshawn Crawford, 21 of East New York, and Keith Luncheon, 24, of Crown Heights, face charges of second-degree murder, second-degree criminal possession of a weapon and first-degree reckless endangerment, in connection with the Sept. 7, 2015, shooting of Carey Gabay, 43, during a predawn celebration before the West Indian Day Parade.

Despite a crowd of street revelers at the J’Ouvert Festival — a Crown Heights precursor to the popular parade hours later — the three engaged in a gunfight stemming from a gang turf war, said Brooklyn District Attorney Kenneth Thompson Wednesday at a news conference attended by NYPD Commissioner William Bratton.

A bullet struck Gabay in the head about 3:40 a.m. as he walked with his brother on Bedford Avenue between Sullivan Place and Montgomery Street in Crown Heights, the NYPD said after the shooting.

Gabay, a Harvard-educated lawyer and the first deputy general counsel for the Empire State Development Corp., died nearly 10-days later after being taken off life support at Kings County Hospital Center in Brooklyn.

“These defendants are charged with creating a killing field in a crowd of innocent people, showing depraved in difference to human life and causing the death of Carey Gabay, who used his Harvard education and commitment to public service to improve the lives of others,” Thompson said in a statement accompanying his announcement of the charges.

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All three defendants were ordered held without bail after pleading not guilty to the charges Wednesday before Brooklyn State Supreme Court Justice Vincent Del Giudice, said a spokesman for Thompson. Alleyne had initially been arrested last month on a criminal complaint but is now covered by the indictment.

A fourth man, Stanley Elianor, 25, of Brownsville, had been arrested last year on weapons possession charges only, said officials.

The gunfire erupted as part of turf battle between the street gangs, Folk Nation and 8-Trey, investigators said.

Members of the 8-Trey group were walking up Montgomery Street, apparently to attend the festivities, when they encroached upon the area outside the Ebbets Field Houses, which the Folk Nation considered its territory, Thompson said.

Surveillance cameras captured images of Alleyne, a reputed Folk Nation member, running from a patio ledge holding a gun, investigators said. Crawford, a reputed ally of Folk Nation, was seen on video running from the street and pulling out a gun. According to witnesses, Luncheon, an alleged 8-Trey member, also displayed a gun, officials said.

Thompson said the three defendants are charged under the depraved indifference murder concept with the theory being they engaged in “mutual combat” that took the life of another.

Alleyne, Crawford and Luncheon faces 25 years to life in prison if convicted. Elianor faces up to 15 years.