Convicted killer Derek Sam could soon be charged by Queensland police with the deaths of two other women, nearly two decades after they disappeared.

Sam is currently serving a life sentence for the murder of 16-year-old Nambour schoolgirl Jessica Gaudie in 1999.

Jessica was kidnapped and murdered by Sam while she was babysitting his three children for his estranged partner at their Sunshine Coast home.

Jessica Gaudie, 16, was murdered when she was babysitting Sam's children. (AAP)

Although her body was never found, a jury convicted Sam of her murder and he was given a mandatory life jail term.

He now stands accused of killing two other women, British backpacker Celena Bridge, 28, and teacher's aide Sabrina Glassop, 26.

Teacher's aide Sabrina Glassop and British backpacker Celena Bridge have never been found. (AAP)

Ms Bridge was last seen walking along Booloumba Creek Road in 1998, while Ms Glassop disappeared from her home on the same road in 1999.

The bodies of the two women have also never been found.

"We need closure for the other two women in order to get closure for ourselves,” Jessica’s sister, Tammy, told 9NEWS.

Derek Sam (pictured in 2001), could soon be charged with the deaths of two other missing women. (AAP)

“I've always believed that they're together somewhere."

Police believe Sam sexually assaulted and strangled all three women, and are now preparing a brief of evidence for the Director of Public Prosecutions.

Detectives took Sam out of jail last year to bring him to Booloumba Creek Road, however he denied any involvement in their disappearance.

Jessica’s mother, Pauline, said she hopes the body of her beloved daughter, who would have turned 34 years old today, is soon recovered.

"It’s very hard that we can't all be here together,” Mrs Gaudie said.