Killer uncle says he can't remember attack

A Sydney man claims he has no memory of fatally stabbing his niece and dumping her body in a blowhole 100km away.

Derek Barrett, 29, previously pleaded guilty to murdering Chinese university student Mengmei Leng, whose naked body was found floating face down inside the blowhole at Snapper Point on the NSW Central Coast in April 2016.

The former IT worker also pleaded guilty to another 21 offences including 19 counts of filming Ms Leng for sexual gratification when she was bound and gagged before her death.

Ms Leng, 25, had lived with Barrett, her aunt and her cousin in the southwest Sydney suburb of Campsie since arriving in Australia to study, five years before her murder.

At the NSW Supreme Court on Wednesday Barrett claimed he was drug affected when he killed Ms Leng and can only remember having an argument with her then seeing blood in the sink.

"You have no idea how it frustrates me every day trying to think of how this came about and why I went down this path," he said.

Barrett is due to be sentenced on Friday.