This past June, an Australian judge sentenced a man found guilty of manslaughter in the 1988 death of 27-year-old American Scott Johnson to nine years in prison. The culmination of the case brought some peace for Scott’s brother, Cambridge resident Steve Johnson, and his family after years of seeking justice.

The saga of Scott’s death — his body was found at the bottom of a 200-foot cliff, below the spectacular site of a seaside promontory known as a gathering spot for gay men — and his family’s quest to solve the mystery surrounding it is the subject of “Never Let Him Go,’’ a four-part ABC News Studios documentary series co-directed by Jeff Dupre and Jacob Hickey that premieres Wednesday on Hulu.

For Steve Johnson, a second recent development meant nearly as much as the sentencing: the conviction of the man who murdered Raymond Keam, who was beaten to death in 1987, during a rash of unsolved hate crimes in Australia against men who frequented gay “beats’’— areas known for sexual activity.

“These cases aren’t so impossible to solve,’’ Johnson said on a recent video call. “Right after Scott’s killer was apprehended in 2020, there was a big surge in public interest to get after these other cases. There was a million-dollar reward posted for Raymond Keam’s murder.’’ Soon after, a family member turned in the killer, he noted.

The murderer was convicted within days of the sentencing of Scott Johnson’s assailant.

It’s been a very long haul for Steve Johnson, who has been making regular visits to Australia for years to investigate his brother’s death and to try to convince the police to take his findings seriously.

“The good news is that the public is beginning to trust the police,’’ he said with an ironic smile. “We’ll see what happens. For a while there, I was hearing from families every week.’’

After his brother’s story was featured on an Australian newsmagazine program in 2013, Johnson met with one family at the spot where a sibling had been murdered. They’d participated in “a 90-second inquest,’’ he recalled.

“The police said, ‘How about suicide?’ The mother started crying. ‘How about an accident?’ And the father started crying.

“‘OK, we’ll call it a mystery.’ That was the entire inquest.’’

But Johnson’s dogged pursuit of the truth about police indifference to the deaths, carried out in part by his Colorado-based colleague Dan Glick, an investigative reporter formerly with Newsweek, has helped move public opinion in Australia. Alex Greenwich, a parliamentary legislator who is openly gay, has credited the story’s ongoing presence in the media as a factor in the country’s 2017 legalization of same-sex marriage.

Though he’s been gone for more than 30 years, Scott Johnson’s presence hovers over the series, through family photos and home movies. At one point, we see grainy footage of a kindergarten-age boy happily wandering through the crowd at a county fair near their home in southern California, forging his own path and oblivious to his parents’ whereabouts.

As a young man, he was a brilliant mathematician who shared his older brother’s love of outdoor adventure and intellectual curiosity. Steve Johnson is a successful high-tech entrepreneur who was a pioneer in what we now know as streaming media. He earned a Master in Public Policy degree from Harvard in 1985.

According to Steve, Scott was a shy, quiet person who tended to avoid the camera. There are pictures, but we do not hear his voice.

“One of the things we used to do — it’s kind of goofy — we’d read the Platonic dialogues together,’’ said Johnson. “We used to record those. I’ve long thought I need to go find those tapes.’’

Johnson’s two sisters, his adult children, and his wife of 45 years, Rosemarie, all appear on camera.

“My daughters are both gay, and they’re pretty proud of the good that has come out of their uncle’s death,’’ he said. “They’d prefer to have known their uncle, but they can see that he’s grown to be an emblem about the lack of police protection, and the homophobia that still exists in the police force.’’

In June, the Provincetown International Film Festival presented a special screening of the first two episodes of “Never Let Him Go.’’

“It was the coming out of the film,’’ said Johnson. “There were a lot of tears in the audience.’’

“The story was still unfolding even as they were making it,’’ said Lisa Viola, PIFF’s artistic director (and also director of programming for the GlobeDocs Film Festival). “In Provincetown, it was a natural fit.’’

Some in the audience had been following the news about the case, she said, “but to see the visuals and hear the voices come to life, it was not just meaningful — it had quite an intense impact. It did not surprise me that tears would be flowing.’’

Johnson’s persistence in pursuing justice is a recurring theme in the documentary, as it has been throughout years of news coverage.

“I think I’ve always been this way,’’ he said. “When our parents split up and we had no money, Scott and I had three paper routes to help pay the rent. I got into college because I learned how to play the clarinet and got recruited to the University of Southern California.

“You really can’t be an entrepreneur if you give up easily. Same with mountain climbing,’’ which he and Scott loved to do together.

But Johnson claims that he can only take “half the credit’’ for seeing the case to its conclusion.

“The police have to take the other half, for forcing me to be persistent,’’ he said. “They could have solved this in the first week.

“They’re the ones that made this a famous story,’’ he said.

James Sullivan can be reached at jamesgsullivan@gmail.com.