Michelle Leng, whose naked body was found floating in the Snapper Point blowhole. Credit:Facebook

Barrett pleaded guilty to the murder of Ms Leng, also known as Michelle Leng, in Burwood Local Court on Wednesday, and to taking photographs of her while bound and naked.

It is not known how far Barrett had advanced in the process of murdering his niece when his adult stepdaughter entered the unit on the afternoon of April 22, 2016, but the two cousins did not clap eyes on one another.

The stepdaughter was home for a little over three hours, during which she told police Barrett remained in the bathroom with the shower running the entire time, apart from one quick trip to the bedroom.

She knocked on the door at one stage to ask for some shampoo and he opened the door a crack to pass it out, warning her that she should use the other bathroom because that one smelled.