The rookie cop who gunned down an unarmed man in the stairwell of a Brooklyn housing complex has turned himself in to authorities​ to face charges including second-degree manslaughter.

Stern-faced Officer Peter Liang emerged about 7 a.m from his Bensonhurst home and​ got into an SUV that took him to ​the 84th Precinct​ in downtown Brooklyn.

He had no comment.

Liang, 27, is expected to be arraigned later in Brooklyn Supreme Court.

A day earlier, a Brooklyn grand jury handed up an indictment on several charges including criminally negligent homicide, assault, reckless endangerment, and two counts of official misconduct.

The top charge of manslaughter is punishable by up to 15 years behind bars.

Authorities said Liang fired his service revolver in the unlit stairwell of an East New York apartment building Nov. 20 during a routine patrol, killing unarmed father of two Akai Gurley, 28.

Liang did not testify before the grand j​​ury, which was convened last week, but Gurley’s domestic partner and a woman who was in the stairwell with him when he was shot both took the stand, a law enforcement source said.