Stymied investigators probing the unsolved Gilgo Beach murder appealed to the public Thursday for help identifying a belt found early in the nine-year investigation.

Suffolk Police Commissioner Geraldine Hart displayed photos of a portion of the black leather belt showing the embossed letters “HM” or “WH” during a news conference in Yaphank.

“We do believe that the belt was handled by the suspect, and did not belong to any of the victims,” she said.

Hart wouldn’t say if there were any suspects in the killings, which were discovered when the remains of eight women, a man and a female toddler were found along Ocean Parkway and nearby in 2010 and 2011.

Authorities have previously said the slayings were the work of at least three killers, with the area around Gilgo Beach having “been used to discard human remains for some period of time.”

Hart called the belt a “significant piece of evidence” that was “recovered during the initial stages of this investigation” but wouldn’t say when or where.

She also wouldn’t say if it held any DNA or was believed to have been used against any of the victims, several of whom were sex workers who authorities have said were strangled and some of whose bodies found wrapped in burlap bags.

Hart announced the launch of a website, gilgonews.com, to accept anonymous tips and provide updates on the probe.

Asked why authorities waited so long to reveal the existence of the belt, Hart said, “So, we are constantly evaluating the investigation. We’re looking at the steps we’ve taken. We’re looking at the technology that’s available at the time. And we made a decision as a team that now would be the time to release this information.”

The news conference — which Hart ended abruptly amid questions from reporters — was held the same day that Netflix released an online trailer for “Lost Girls,” a movie based on a 2013 book about the case.

The feature is set to premiere at the Sundance Film Festival on Jan. 28, and be shown in select theaters and streamed online starting March 13.

Thursday’s announcement also came ahead of a Tuesday deadline in an appeal by the Suffolk County Police department of a judge’s 2018 order to hand over recordings of 911 calls made by sex worker Shannan Gilbert, 23, whose disappearance led to the searches that turned up the bodies.

Gilbert — whose skeletal remains were discovered in December 2011, more than 19 months after she went missing — isn’t officially counted among the homicide victims because an autopsy was inclusive.

Hart said Thursday that Gilbert’s death “does not match the pattern of the Gilgo Beach homicides.”

Gilbert family lawyer John Ray, who’s waged a four-year court battle to get the 911 recordings, called the news conference “utterly meaningless.”

”The police always had that piece of evidence, so why didn’t they release it in nine years and suddenly do so now? And don’t describe it?” he said.

Ray said he’d met with Netflix about the “Lost Girls” movie and while he hadn’t seen the movie, “It appears they’re creating a heroine out of [mother] Mari Gilbert in pursuing her daughter in the face of police resistance.”

Ray described the news conference as an attempt to “get ahead of the [appeals] court decision and the criticism that will cascade down upon the police because of the film as well.”

Several former Suffolk County investigators, who didn’t work on the Gilgo Beach murders, were astounded to learn that the belt was discovered but never revealed to the public.

“I can’t believe they sat on it so long,” one ex-cop told The Post.

“You’re looking for it to help you solve the case now — wouldn’t it have been smarter to do this nine years ago?”

Another ex-cop said that “as far as an investigation goes, its always better to put out information when it’s fresher in people’s minds when you’re looking for help from the public.”

“People forget something that happened nine years ago,” the source added.

Some key law-enforcement figures in the Gilgo Beach probe have wound up in the wrong side of the law in recent years, with former Suffolk Police Chief James Burke pleading guilty in 2016 to beating a suspect who had stolen a stash of porn and a sex toy from his official vehicle, then forcing his subordinates to cover up the incident.

Burke, who was sentenced to 46 months in federal prison and released in April, stonewalled the FBI’s efforts to probe the Gilgo Beach murders “because he knew we were investigating him,” a federal source told The Post following his 2015 arrest.

In 2016, a prostitute who identified herself as “Lee Ann” also publicly claimed that Burke had “rough sex” with her and that she’d seen him “grab a girl by her hand and drag her to the group” during “sex parties” in Oak Beach.

Former Suffolk County District Attorney Thomas Spota and his former chief of investigations, Christopher McPartland, were convicted last year for conspiracy, witness tampering, obstruction of justice and being accessories after the fact in Burke’s case.

They each face a maximum 20 years in prison when they’re sentenced in April.