The fascinating backstory of the detective who won't give up on William Tyrrell. 

It was a warm Spring day, on September 12, 2014, when a little boy named William Tyrrell was playing hide-and-seek with his sister in the front yard of his foster grandmother’s home in Kendall, New South Wales.

His mother and grandmother watched as three-year-old William ran around in his Spider-Man suit, just before 10:30am, at one point imitating a tiger and yelling, “raaaarrrr” before running down the side of the house.

And then, there was silence.

His mother went inside to make herself a cup of tea, but was quickly struck by how quiet things had become. Five minutes later, she started calling out for him, searching the yard and inside the house for her little boy.

It took her less than 30 minutes to call emergency services, and no more than 10 minutes for them to arrive.

These were the preliminary pieces of the puzzle Detective Chief Inspector Gary Jubelin had placed before him three years and nine months ago.

Since then, he has led a team who have identified 700 persons of interest, gathered more than 4000 pieces of evidence, received more than 15,000 pieces of information and conducted hundreds of interviews in an effort to answer the question that has weighed heavily on him: What happened to William Tyrrell?

This week, under the direction of Chief Inspector Jubelin, police began a four week forensic search for William, armed with chainsaws, rakes and hoes, focusing on a specific three kilometre area of bushland near where the three-year-old was last seen.

But this is not the first high profile case the detective has led - and if anyone is going to discover what happened to William, at approximately 10:30am in September, 2014, Chief Inspector Jubelin is the person equipped to do it.

Listen to The Quicky debrief on the truth about William Tyrrell's parents, and what happened after the three-year-old's disappearance. Post continues below.

At 22 years old, Jubelin was working on a building site when he saw, out of the corner of his eye, police chasing down a "bad guy". With no sense of what he wanted to do with his life, Jubelin remembers thinking that looked like something he might just be interested in.

He applied the following day.

As he filled in his paper work, unsure of what the job consisted of, it's unlikely he imagined he would one day be played by a famous Australian actor, in one of the country's most acclaimed true crime-drama series.

In 2012, actor Matt Nable played Dept. Insp. Gary Jubelin, a protagonist in Underbelly: Badness, which covered a number of real crimes that occurred in Sydney between 2001 and 2012. Under the direction of Anthony Perish, a convicted kidnapper, murderer and drug-dealer, a flurry of criminal activity took place in Lindfield, New South Wales.

It was only due to the perseverance and commitment of Jubelin, that Perish was ever caught and prosecuted.

And that is what he has become known for.

In 2016, Jubelin was presented with a perplexing case that involved a 25-year-old woman, Michelle Leng, who was found naked, lying face down and floating in a blowhole at Snapper Point in New South Wales.

Jubelin appealed to the public in a press conference, urging anyone with any information to come forward, because perhaps they would have "a piece to a jigsaw puzzle," that he would work tirelessly to complete.

In the months that followed, detectives began looking more closely at her uncle who she was living with, Derek Barrett, and discovered footage on his mobile phone of him masturbating over his niece as she slept.

And there was more.

Barrett had filmed Leng showering in their Campsie home, and had kept images of her naked, bound and gagged, moments before - it was later discovered - he murdered her.

By December 2017, Barrett had been sentenced to 46 years in prison, after being found guilty of stabbing his niece 30 times and dumping her body.

Standing outside the courtroom, Detective Jubelin said, "The courts have recognised the seriousness of the offence by the sentence that was handed down on Mr Barrett.

"From an investigative point of view it is satisfying that we've got justice, but there is no joy in a matter like this, it's just an extremely sad case."

Detective Jubelin, a father of two, has also been instrumental in investigating the Bowraville murders, an unsolved case where three Indigenous children disappeared from the same street between 1990 and 1991.

Justifiably, members of the Bowraville community have an intense distrust of police, but Jubelin has managed to earn the respect of the aggrieved families.

In 2014, he said of the case which he had been working on for more than eight years, "I am still shocked by the lack of interest that has been shown in this matter."

The family, he believes, has been "let down by the justice system."

As it stands, there is a $1 million reward for any information leading to William's recovery, more than three years since he mysteriously disappeared.

Detective Jubelin has a list of persons of interest, and says that list is "constantly being added to."