University graduate Michelle Leng was stripped naked, bound and gagged before her uncle allegedly stabbed her and dumped her body in a blowhole on the NSW Central Coast.

The horrific details of Ms Leng's final hours have been revealed after detectives laid further charges against her uncle Derek Barrett on Wednesday.

Ms Leng's body was found floating face-down in the Snapper Point blowhole in the Lake Munmorah national park on Sunday, April 24.

At the end of April, homicide detectives charged Mr Barrett, 27, who lived with Ms Leng, 25, in Campsie, with murder.