By Denise Glass
Tayside reporter, BBC Scotland news website
A father faces a lengthy jail term after having two children with his eldest daughter and sexually assaulting her sisters.
The 72-year-old, who cannot be named as it would identify his victims, abused the children in Dundee and Fife between 1976 and 1993.
Michele Elliot believes abusers make their victims too scared to tell someone
The case, and similar ones which have come to light recently, has raised questions about why no-one knew what was happening and the long-term affect it would have on those involved.
Michele Elliot, chief executive of the charity Kidscape, said: "The trouble with people like this man is they terrify their families, they keep them in such conditions that they won't tell.
"They're scared to tell on him, the father has told them that if they tell something terrible will happen to them, for example their children will be taken away.
"The kids - you can't believe it - they go out, they go to school, they go with various people, but they still don't tell."
The man's wife had also been accused of abusing the girls, but her not guilty pleas were accepted by the Crown.
Ms Elliot said: "Of course we're very angry with the mothers in these cases saying, 'how could you let this go on?'"
"But they're often in fear for their lives, they've been beaten down over the years by this very controlling horrible man who may to the outside world appear to be an okay person."
Former Conservative party leader Iain Duncan Smith set up the Centre for Social Justice think tank. He believes that society must take more responsibility in cases like this.
He said: "What is required here is a system that allows people to have common sense.
"For example, if a doctor sees a child and thinks that child is being abused then the doctor should alert the social workers.
"Similarly, if a teacher thinks that a child is missing school a lot, coming back with bruises or whatever, not looking right, they're a bit down again, they should alert them to say, 'well that's worth looking at'."
The culprit in this case was eventually caught when his eldest daughter went to the police after her children had grown up.
Christiane Sanderson, a psychologist specialising in counselling victims of sexual abuse, believes the daughters may be able to recover and form trusting relationships if they are given the right support.
She said: "Resilience built up over the years is one of the most critical factors and that's got to be supported by being heard and believed, being paid the attention that is necessary.
"I think it takes a tremendous amount of courage for an incest survivor or indeed any victim of child sex abuse to make a disclosure, even though it's many years down the line.
"That really is the beginning of the recovery process which needs to then be supported by good professional, sensitive, counselling in order to enable these individuals to heal from what has been a very tortuous experience."
Ms Sanderson believes there are other children out there who are suffering the same kind of abuse from their fathers.
She said: "Sadly there are many cases where this is occurring as we speak and has done historically.
"It's much more common than we'd like to think."
The culprit in this case will be sentenced next month.