Trudie Adams' disappearance haunted many. Now a sickening side to the story is emerging.

Trudie Adams was 18 when she went to a party at the Newport Surf Lifesaving Club, asking her mum, Connie, to wait up for her.

It was a Saturday night in June, 1978.

When Trudie left the Newport dance party early, she planned to hitchhike home – as many young women did back then – and just after midnight, her ex-boyfriend, Steven Norris, saw her get into a car on Barrenjoey Road. It was the last time anyone would ever see Trudie Adams.

In the 40 years since her disappearance, a man named Neville Tween has long been the prime suspect in Trudie’s presumed murder. He was, however, never asked a single question about the case until 2009 – despite being suspected of two murders in the ’80s, and being charged with more than 100 crimes – many of which took place on the northern beaches.

So why wasn’t he questioned?

According to Unravel, an ABC podcast about the disappearance of Trudie Adams, Neville Tween had close ties to Australian Federal Police officer, Mark Standen. While this friendship likely hadn’t emerged in the late 1970s when Trudie first went missing, the connection between the two was reportedly clear by the time of a 2008 police investigation into Trudie’s case.

When NSW detective Jayson McLeod started to look into a number of northern beaches crimes in 2008, he turned to the Crime Commission’s top investigator, Mark Standen.

“I provided Mark Standen with my investigation plan, as to how I was intending to gather evidence against Tween,” he says on Unravel.

McLeod says over the next few weeks, Standen seemed to be delaying any action into the case.

It was then that McLeod claims he discovered that Standen’s son, Matthew, had applied to join the NSW Police Force, using Neville Tween as a reference.

Both Mark Standen and his son Matthew deny this story.

Standen acknowledges only that he knew Tween.

Between 2008 and 2010, cold case detective Gavin McKean re-investigated Trudie Adams’ case ahead of the 2011 coronial inquest into her disappearance.

He says he has little doubt that Tween, who died in jail in 2013, is responsible for Trudie's murder. Several women at the time reported attacks by a man who fit the description of Tween, and after Tween moved to the NSW central coast, the attacks stopped.

For journalist Ruby Jones, telling this story has been about shining a light on our justice system.

"I've always been interested in crime and also looking at violence against women," Jones told Mamamia, "[but] more broadly, for me, there's a sense that you want to know that if something bad happens, to you or to someone who you care about, that the systems are in place and the systems work, and the police will investigate properly and if they don't, that there will be repercussions."

"That the justice system, you know, it will do its job. So when that doesn't happen, people want to know why, and I think that's part of the reason they're so invested in finding out what happened to people like Trudie.

"There were a whole lot of things about this case that hadn't really been made public before," she said. "So there's all these kind of questions that we wanted to ask that we think are very much in the public interest and they go towards policing and the justice system and I guess the organised crime world and connections between the two.

"And that also goes to, I guess, not only what happened to Trudie but also why there hasn't been justice for 40 years."

Throughout Jones' investigation, she's received correspondence from "at least a dozen" women who had disturbing encounters on the northern beaches around the time of Trudie's disappearance.

Overwhelmingly, these women didn't report their experiences because they thought they'd get into trouble.

"No one's really been brought to justice for those attacks either," Jones says, "so it's still open".

With women still contacting the ABC with their own close encounters, it's unclear where Jones' investigation will go.

But there are questions being asked, and lines of inquiry followed, that never have been before.