A man jailed for murdering his niece whose naked body was found floating in a NSW blowhole has admitted repeatedly raping the gagged and terrified woman after video of the attacks was found on a USB.
The carer of a woman with dementia found the USB in her hand in November 2019, but a judge has been told Derek Barrett had given no explanation of how she could have obtained it.
Justice Helen Wilson previously found Barrett had filmed his attacks but deleted them from his phone on arrest from fear of detection.
The now 32-year-old was jailed for at least 34 years and six months in 2017 after admitting repeatedly stabbing student Mengmei Leng, whose body was found in the blowhole at Snapper Point on the Central Coast in April 2016.
He had admitted filming the 25-year-old niece of his wife, while she was bound and naked, for his sexual gratification.
"This was a despicable crime of extreme brutality and great wickedness," Justice Wilson said when jailing him for a maximum of 46 years.
Barrett faced a sentence hearing in the NSW Supreme Court on Wednesday after pleading guilty to nine charges of assault with acts of indecency and aggravated sex assault, committed on April 22 2016, before he stabbed her at least 30 times.
He asked the judge to take into account a further eight similar offences.
Prosecutor Huw Baker SC said the Crown had failed in a bid to re-open its case by having the fresh USB evidence presented to Barrett's unsuccessful sentence appeal hearing in 2019.
The Crown had submitted it was relevant to the appeal as it was capable of showing Barrett "repeatedly violently sexually assaulted his victim whilst she was restrained and, in so doing, derived pleasure from the pain, distress and suffering of the victim".
Forensic psychiatrist Dr Richard Furst, who gave evidence at the murder sentence hearing, on Wednesday testified that his updated opinion was Barrett possibly had a schizoid personality disorder or an autism spectrum disorder,
Noting the videos showed the victim gagged and bound "with a look of horror" prior to her death, he also referred to Barrett having a voyeuristic disorder and a sexual sadism disorder.
Dr Furst said he had repeatedly minimised his actions, saying he had no idea why he gagged and bound his niece, and had exaggerated his use of the drug ice.
He referred to Justice Health records which noted he suffered from depression, but he believed this was due to his situation in jail.
Barrett was recorded as having said it had been "one bad episode and he was not a psychotic killer", as well as contending he had consensual sex with his niece - which was contradicted by the videos.
His barrister Andrew Norri will call defence psychiatric evidence when the hearing resumes on February 9.
