In 2021, the serial paedophile Ashley Paul Griffith wrote a letter to parents of children at a Brisbane childcare centre, where he was employed as the director, addressing claims on social media the centre was “involved in a pedophile ring”.

“We want to reassure families that the wellbeing and safety of you and your family are of paramount importance,” wrote Griffith, who had set up a tripod camera inside the centre so he could film his sexual abuse of young girls from two different angles.

“We take child protection extremely seriously.”

On Friday, Griffith was sentenced to life in prison for 307 sexual offences against 73 victims, mostly young girls aged between three and five. Most of the offending occurred while he was employed at childcare centres in Queensland between 2003 and 2022.

Some victims and their families told the Queensland district court that they trusted and grew close to Griffith; one mother said she had “invited him into our home, into our life, and into our family”. Others are now questioning how, as Griffith’s abuse “escalated”, warning signs were missed.

In 2021, Griffith was the director of a childcare centre and notified authorities about an allegation that a female colleague had inappropriately touched a young girl. Police investigated but took no action.

About six months later, police interviewed Griffith in relation to another disclosure by a young girl. He denied the allegations at the time and was not charged.

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In early 2022, Griffith moved to work at a different centre. There, a three-year-old girl made disclosures that were investigated by police, who found they “did not meet the necessary threshold for a criminal investigation”. Griffith had his shifts cancelled, but he was not charged.

The Australian federal police eventually learned all three girls had been abused by Griffith. He had recorded himself sexually assaulting or raping them – and 70 others – over a period of almost 20 years.

Dark web user ‘Zimble’

Since 2013, authorities had been searching for a man named “Zimble”, a dark web user who had uploaded child exploitation material to a now defunct paedophile community. The server required users to upload content in order to gain access to other material.

Zimble was briefly active in the community. He posted several videos and made comments advising others how to offend against young girls. He said that he acted in a way that sought “a balance between minimising risks and seizing opportunities”.

Authorities spent almost eight years searching the globe for Zimble until a breakthrough in 2022 led them to Griffith. They identified in one of his posts a type of blanket that had been sold to childcare centres in Queensland. They matched videos to locations and searched staff lists. That led them to his Gold Coast home in August 2022 and the discovery of a trove of videos documenting his abuse.

The files on Griffith’s computer included class photographs and enrolment details of children he had offended against. In some cases he had spliced videos together. Files were named by the type of sexual activity depicted.

A psychiatrist told the court Griffith had a “paedophilic disorder” and that he lacked empathy to the victims.

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Summarising the psychiatric report, the district court judge Paul Smith said Griffith “never tried to stop the offending because he did not have the courage to do so”.

He said Griffith’s offending “was chronic and escalated over time”.

‘Ignored the signs’

The court heard from more than a dozen people, including young women who were abused as girls and the parents of more recent victims. Some have chosen never to tell their children they were abused.

Some spoke about their anger at church organisations and childcare providers for not preventing the abuse.

Outside the court on Friday, the father of a victim addressed reporters on behalf of victims and said the verdict marked “the end of a long journey” that begin in 2022, when families were first notified about the abuse by the Australian federal police.

“There are businesses, staff and regulators who ignored the signs, who didn’t follow through on reports, and failed to supervise our children,” the man said.

“We hope that the Department of Education investigates these centres and holds those responsible accountable for their negligence. The community deserves to know that these people will never work with children again.”

Smith said Griffith was “depraved and has a high risk of reoffending”. He tendered a “letter of apology” to victims and sat silent and emotionless through most of the hearing, as family members of victims wept in the gallery behind.

Griffith will be 71 when he is eligible for release from the high-security Wolston prison.

• In Australia, children, young adults, parents and teachers can contact the Kids Helpline on 1800 55 1800, or Bravehearts on 1800 272 831, and adult survivors can contact Blue Knot Foundation on 1300 657 380. The crisis support service Lifeline is 13 11 14. In an emergency, call 000. International helplines can be found via www.befrienders.org