William Tyrell investigation was doomed with laws around foster children ...

The baffling disappearance of William Tyrell was hampered from the very beginning with strict privacy laws around the foster care system making the job of investigators much more difficult, one of the state's top cops has revealed.

Former Deputy Commissioner of the NSW Police Nick Kaldas admitted to 7News Investigates that in the early stages the restrictive laws hindered police and raised 'scepticism' in the community as detectives were banned from publicly identifying members of William's biological and adopted families. 

The three-year-old went missing without a trace from a Kendall property on the NSW Mid North Coast on September 12, 2014, sparking one of the largest police investigations in Australian history.

Young William disappeared from his foster grandmother's Benaroon Drive home while playing in the yard in a Spiderman suit.

Seven years on, a two-part documentary has teased new evidence will be revealed next week which could finally shed light on who was responsible for the suspected abduction.

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William and his five-year-old sister had made the five-hour drive from Sydney with their foster parents. 

His foster mother, who cannot be identified due to legal reasons surrounding the identification of foster carers, had only taken her eyes off William for 'five minutes'. 

Mr Kaldas said the strict state laws put in place to protect the privacy of those in the foster care system, made the job of detectives much harder than usual.

'It made it very difficult for the initial investigative police holding press conferences and briefings because they were tip-toeing around the issue because of privacy reasons and legal reasons and it made them look like they weren't telling the whole story,' he said.

'It was incredibly well intentioned and they were doing the right thing by abiding by what you can and can't say about children, particularly when they've been in foster care. But It was a very difficult situation for those who dealt with it initially.'

It was also frustrating for the media desperately trying to get the message out, as they were hamstrung by the unusual circumstances which surrounded the case.

'It was extremely confusing and I think from the very beginning it really hindered and hurt the police case,' veteran Channel Seven journalist Michael Usher told the program.

To make matters worse the public were growing increasingly sceptical. 

'Even I remember thinking this is all very strange, there is something they aren't telling us,' Usher said.

'It was difficult to tell the truth about William's status because he had foster parents, he had biological parents, he had Family and Children's Services involved and they also had an outside agency partly caring for him as well.

'And then you had the police involved, so this poor little boy was lost in and amongst all of that and his message and his story wasn't able to be told properly.

'All of those early traditional of a search and a public appeal campaign… none of it could happen.' 

William's foster mother had been outside with the energetic child but returned to the kitchen to make a tea.

William was constantly 'roaring' like a tiger while running around outside but when he mysteriously stopped, his foster mother became felt something was wrong.

She rushed out the door but there was no trace of the blonde-haired boy. 

In the moments that followed she frantically called Triple-0 and within hours hundreds of officers, volunteers, SES and RFS members were scouring nearby bushland that backed onto the property.

Detectives conducted multiple searches around the home and in surrounding areas but no significant clues were ever found and search dogs came up with nothing.

Consensus among police is that William was snatched in an opportunistic attack.

Detectives continue to investigate a number of suspects and theories, including whether the little boy was kidnapped by a member of a paedophile ring. 

William was sent to live in foster care because his biological parents had issues with drugs and alcohol as well as domestic violence.

But his biological mother says the two were in the process of getting their lives back on track after William was born.

She said the laws which have essentially silenced her from making a public appeal in which she can be identified are 'cruel'.   

'I don't care about my privacy. It got me nowhere. I want to stand up and tell people the real story,' she said.

'Because I haven't come out and said anything people are going to assume I don't care.

'It makes me angry. Angry at the system.'     

The NSW Government in 2016 announced a $1million reward for information that leads to the recovery of William.

In March 2019, a coronial inquest launched into William's death, which remains ongoing.