Mother of five Denis Hofman had just heard the shocking news that her friend Michael Guider had been arrested in March 1996 for the sexual abuse of children on Sydney’s Northern Beaches when her phone rang.

It was another acquaintance, a journalist who claimed Guider had confessed to her that he’d known nine-year-old Samantha Knight, missing for 10 years, and her mother Tess `quite well’.

Guider had confided in the woman that he often visited the site at Bondi where Samantha vanished and wanted to find the ‘truth’ about what happened to her.

The revelation immediately raised red flags for Hofman who begged her friend to go to the police.

But for reasons Ms Hofman still finds difficult to understand, her friend declined due to her friendship with Guider.

CHAPTER 1: HOW INMATE HELPED CATCH KILLER MICHAEL GUIDER

This sparked a near decade-long crusade to bring Guider to justice and one that would see her go head-to-head with some of the most senior police in NSW as she battled to convince them her former friend was a monster.

The pair had spent many days over the previous three years exploring bushland around Sydney and documenting significant Aboriginal heritage sites, especially in the city’s northwest.

Guider had snatched the nine-year-old off the streets near her Bondi home on August 19, 1986. He gave her a can of soft drink laced with drugs to render her unconscious while he took photographs of her. But when she began to wake he gave her another fatal dose.

He would eventually plead guilty to manslaughter and was jailed for 17 years.

Ms Hofman’s first step was to report the connection to police in Castle Hill. But when she wasn’t satisfied with her response she decided to take matters into her own hands.

Unbeknownst to her family, Hofman began visiting Guider in Lithgow Jail where he was serving a 16 year jail sentence for assaulting young girls.

Her aim was to subtly illicit a confession.

Such was his ability to manipulate people, Ms Hofman said she went away from those initial visits feeling like police may have the wrong man.

He would write to her in between visits and reminisce about their days in the bush.

“That’s all that keeps me going, locked in prison cells, the hope and faith that one day in the not too distant future I can go bush again with friends like you,” he wrote in one letter that Ms Hofman recounts in her book Forever Nine.

It soon became obvious that all this was part of his pattern of manipulation and deceit. He did consider Ms Hofman as a friend in the beginning, but he also understood those letters would be read by others.

She kept visiting, more than a dozen times in total, but the man she describes as a ‘complete sociopath’ never gave anything away. He became aware of what she was trying uncover after a police officer mentioned her name while questioning him.

“I went to talk to Guider and I find out that two cops from Bondi had given him my name and the man who went along with me,” she told the Telegraph.

Ms Hofman claims investigators continued to brush her pleas aside. with one senior officers stating there was no Guider would be charged with Samantha’s disappearance.

“He said at that stage the Samantha Knight case and Guider was never going to go anywhere and we should just go on our way and forget about it,” she said.

It would take a further two years before police finally took Ms Hofman seriously.

Capitalising on the ongoing relationship she had formed with Guider, police secretly bugged the visitors room inside the Lithgow Jail and recorded the pair as they spoke.

But Ms Hofman also believes the police went a step further and bugged her own phones.

“We’d given my phone numbers - mobile and home - to Guider because at that stage we were encouraging him to ring me and he might say something on the phone and that’s all they were interested in,” she said.

Persistence eventually paid off. Further witnesses, including Guider’s own brother, came forward to testify allowing police to bring some closure to the 16-year mystery.

But Ms Hofman is convinced that her former friend is hiding more secrets and believes he should never be let out of prison.

During the investigation, hundreds of scrapbooks were found that had clippings from missing persons cases all across the country.

Ms Hofman has pleaded with police to examine these cases more closely as she believes Guider could hold the key to solving even more cases that have long gone cold.

Years spent chasing down a killer took its toll on the mother of five who wanted nothing more than to bring closure to a case that had haunted the city for so long.

“I would just pull over and cry after some of those meetings with him,” she said.

The endless brick walls she ran into with law enforcement also left a lasting impression on Ms Hofman.

“I’ve got no time for the police, they almost gave me a nervous breakdown, that’s for sure,” she said.