A husband and wife who began a sexual relationship with the man’s 15-year-old daughter because he believed it might help her recover from previous sexual abuse have both been jailed for years by a District Court judge.

WA’s District Court heard today how in 2016 the teenager was placed to live with the couple, both aged 39, at their house in Rivervale by the Department of Community Protection after she was sexually abused while living with her birth mother.

But instead of what Judge Mark Herron said she needed – “protection and affection” – the court heard her father developed a sexual interest in her, and acted on it earlier this year.

After admitting to his wife what he intended to do, he then asked her if she wanted to join in – and eventually she did, engaging in solo sex and group sex with the girl a total of nine times in just over three weeks in March this year.

The court heard it was only when the girl’s school teachers deduced what was going on that police were called in, and the couple arrested and charged with dozens of child sex offences.

They pleaded guilty to them earlier this year, and today were sentenced.

In court the man told psychologists he genuinely believed he would be helping the girl by having sex with her, because she was unable to get a steady boyfriend because her previous abuse.

Prosecutors said that thinking was “cognitive distortion” of the highest order.

The woman told authorities she felt compelled to go along with the sex, because she feared she might be replaced in the marriage by her stepdaughter.

Judge Herron described the abuse as a “gross abuse of trust”, and said the man’s rationalisation of his actions was particularly worrying.

A harrowing victim impact statement from the girl described how she had lost all trust in men and women, and feared she would never fully recover.

The husband was jailed for nine-and-a-half years, with parole eligibility after seven-and-a-half. The wife received a prison term of six-and-a-half years, with eligibility for parole in four-and-a-half years.