A mother and stepfather have been found guilty of raping a girl who was returned to their care after being dismissed as a "troublesome teenager" by social services.
The parents, now both in their 70s, abused the girl from about the age of 10 between 1975 and 1981, during which time the prosecution said social workers in West Sussex rejected her claims.
The jury at Southwark Crown Court on Friday agreed she was telling the truth and that her abuse continued by convicting the man of two counts of rape and the woman of one.
They also found the stepfather - who gasped and muttered "Jesus Christ" at the verdicts - guilty of two counts of indecent assault on her younger sister.
The mother was convicted of rape on the basis she aided and abetted him and it was said she "actively encouraged it". None of parties can be named for legal reasons.
Prosecutor Jose Olivares-Chandler previously said: "You will hear when she was growing up, the complainant did mention this sexual abuse to the professionals around her."
He continued: "Whilst notes were made about it, no-one seemed to have taken her seriously.
"It looks like the word of a troublesome teenager in the late 1970s about sexual allegations was just dismissed at the time."
Jurors were unable to agree fully on the guilty verdicts and returned them on 10-2 majorities for the pair, who will be sentenced on Thursday.
After deliberating for nearly eight hours, they cleared the pair on further counts.
The court heard social workers' notes show they interviewed the man in 1979.
He told them the older stepdaughter's claims were nonsense and said she had "come on to" him.
Both victims, now in their 50s, did not maintain contact with each other and made separate complaints to police, the latter in August 2013 to Merseyside which police matched to one by the younger sister in Dorset in 2011.
The parents had split and the mother was living in Ireland when arrested while her former husband was in Stowmarket, Suffolk.
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