A repeat offender hoarded more than 280,000 child abuse files in a "fixation" centred on "completing the set", a defence barrister has argued.
Paedophile Michael Stanley Cooper, 66, faced the start of sentencing in the ACT Supreme Court on Tuesday.
Cooper has spent more than a year behind bars while on remand.
He previously pleaded guilty to nine charges including possessing and accessing child abuse material, soliciting child abuse material, and failing to report as a registered sex offender.
Last year he was found with more than 280,000 images and videos showing child abuse material, including more than 76,000 unique files depicting at least 1250 victims.
Cooper was well-known to police, having previously amassed the largest number of child abuse files ever seized in the ACT.
In 2010 Cooper was found with almost 700,000 child abuse files, and sentenced to periodic detention that was suspended in 2012.
However, by 2014 he was re-offending and spent the next several years hoarding more abuse files.
Agreed facts for Cooper's latest crimes state he used Frost, a peer-to-peer online encrypted messaging application, to share and download child abuse material with other users on various "boards", using the usernames "Tantalum" and "Blank Frank".
A police search warrant of Cooper's Amaroo home in February 2023 uncovered USBs, computers and external hard drives that contained child abuse material, including about 350 CDs.
The devices contained "highly structured" folders and sub-folders organised by "series" and "model", with the abuse material showing children aged from about three years old to mid-teens.
In a recorded interview with police, Cooper said he didn't agree with the legal definition of child abuse material and had his own opinions "most people wouldn't agree with".
He estimated he had more than 500,000 unique child abuse files, and told police he did not have a sexual interest but "sees it as a hobby or compulsion".
On Tuesday, defence barrister Tahn O'Rourke argued Cooper's "engagement in the collection of child abuse material is somewhat different from the norm".
She said Cooper's motivation for the crimes was a "fixation" related to his diagnoses of autism and paedophila disorder.
"It was directed towards completing the set," Ms O'Rourke told the court.
Cooper had multiple abuse images of the same victims and a "drive to complete the collection", she said.
The defence barrister claimed part of the 66-year-old's motivation arose from "serious social isolation", and discussions with others online "filled the social gap".
Crown prosecutor Kayt Hogan argued Cooper had not been deterred by his previous punishment and had continued "very extensive offending".
"There was an enormous volume of child abuse material and there was an extended duration," Ms Hogan told the court.
"The offender has clearly gained sexual gratification from the offending behaviour."
Justice David Mossop is set to hand down Cooper's sentence next week.
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