I find the last comment non-feasible. Such offenders are lying.I'd be very interested in knowing who funded these 'studies.'
The pattern has been observed across many countries so I doubt it's just one study. Unfortunately, such things tend to be behind paywalls. Some stuff I do find, though:
https://www.psychologytoday.com/us/...evidence-mounts-more-porn-less-sexual-assault
https://www.scientificamerican.com/article/the-sunny-side-of-smut/
Sex offenders commonly report porn helps them keep their desires in the realm of imagination.
My father did extensive work with sex offenders in Australian prisons. He says that all sex offenders were addicted to porn. They get addicted so much that just like drug users the existing 'fix' is not enough. So they increase the dose. For sex offenders this means going from visual imagery to people. He says that there is no safe level of porn for anyone.
If that were the case then we would see an increase in sex crimes with widespread porn. We don't.