Detectives investigating the disappearance of a woman more than 40 years ago have interviewed her step-father who is serving five years in jail for abusing her sisters.

Mary Duncan left her Bonhill home in West Dunbartonshire on March 19, 1976 and has never been seen or heard from since.

Her disappearance was considered completely out of character, particularly as she left behind her 13-month-old daughter.

Yesterday, her three sisters Debbie Renwick, Mandy Duncan and Marion McFarlane have issued an emotional appeal to help find out what happened to their sibling.

Ms Renwick, 56, said: “Somebody must know what happened to her and we hope that person will come forward now."

Ms Duncan, 59, who has never spoken publicly before, said any information from the public could be “the missing piece of the jigsaw”.

HeraldScotland:

Mary Duncan

Detective Superintendent Calum Young also revealed that police had interviewed their step-father Norman Duncan, who was jailed for five years in 2016 for abusing two of the sisters.

Both Ms Renwick and Ms Duncan also last year waived their right to anonymity to speak out against the abuse they suffered.

Detective Superintendent Young said: “Whilst there is no evidence to suggest Mary came to any harm, due to the fact that she has not been seen or heard from in 41 years, we can’t rule this out.”

He said Norman Duncan is just one of a number of lines of enquiry, and they are keeping an open mind about the investigation, which remains a missing person case.

Ms Renwick added: "We are miserable without her. We have missed her every year. She was our elder sister.”

“We just want to bring her home. Please bring her back,” she said.

Ms Duncan added: "Mary matters a great deal even now. She would have been 60 next year. We have missed a whole generation."

Detectives believe local knowledge could be key to finding Mary, particularly former workers of the Vale of Leven Hospital or people who were around the hospital at the time, where she was regularly seen.

Her disappearance was considered completely out of character, particularly as she was devoted to her 13-month-old daughter, Laura, who was to later die of natural causes in October the same year.

Mr Young said: "Her family say Mary absolutely adored her daughter and that her disappearance, and leaving Laura behind, was completely out of character.

“Mary left home with no money and she has never claimed benefits, paid tax or national insurance.

"Her family strongly doubt that she would have had the means or life skills to start a new life and live independently.”

He added: “Mary’s family were left completely devastated by her disappearance, a pain which lives with them to this day, and it is vital that we get to the bottom of what happened to their sister and provide them with some closure.

“I would ask anyone who knew Mary or her family in the years before her disappearance to please get in touch to help us piece together the details of her life around the time she went missing.

“I believe the answer to what happened to Mary lies within the local community."

Those with any information are urged to contact Dumbarton Police Station on 101.

Meanwhile, the sister of a woman who was found murdered at her home nearly 40 years ago has also made another appeal for information.

Brenda Page was discovered in Allan Street, Aberdeen, however has been "brought to justice" over her killing.

Following instruction in 2015 to re-investigate the case, Police Scotland and the Crown Office have continued to carry out enquiries.

Her sister Rita Ling said: "40 years have passed since Brenda was found and not a day goes by when we don't think about her and the horrendous ordeal she must have suffered that night..

"Brenda was an extremely intelligent woman with her whole life ahead of her.

"It pains us to think of the great things she would have undoubtedly achieved.

It is important the police and Crown Office have all potential information available to them to bring the person responsible for her death to court.

"Please come forward if you think you can help."

HeraldScotland:

Brenda Page

Brenda worked in the genetics department at the University of Aberdeen Medical School from 1973 until the 32-year-old's murder in 1978.

Officers have spoken to many of her former colleagues but are now urging any others not previously in contact to get in touch.

Police Scotland said it is trying to build up a picture of what happened in the run-up to Brenda's death.

Detective Inspector Gary Winter, of the major investigation team, said: "I must stress that our enquiries don't just focus on Friday July 14, 1978 and the hours leading up to her body being found.

"It is crucial we build a picture of Brenda's life generally as part of our enquiries, which is where her neighbours, friends and colleagues come in.

"I appreciate this was a long time ago, however if you do remember anything, I urge you to come forward.

"Forensic techniques and processes have changed dramatically over the past 40 years and we continue to use every resource at our disposal to explore information relating to this case.

"It is crucial someone is brought to justice for Brenda's murder."