Few people in the West Bank town of Beit Awwa knew of Vasam Musalmeh and his sister Nawal.
Since they were children the disabled siblings were kept like animals in squalid, crumbling concrete rooms behind their parents’ house.
Before authorities found them last week they had been there for over 40 years.
Disabilities are still regarded as a social stigma in Palestine and the pair were hidden in the fear that they would ruin the marriage prospects of a healthy child.
In a statement, police commander Samih Saify said that while searching the house, officers heard unusual noises and went to investigate. They found Basam Musalemeh, 38, naked and his 42-year-old sister wearing just a flimsy nightdress. The room was said to have stunk of urine and sweat.
The father was arrested although it was not clear whether this was due to the children’s situation or because he had links with the Hamas militant group.
The case has highlighted the shame felt by families who have children with disabilities in Palestinian society – made worse because of poor services and the practice of first-cousin marriages in Arab communities.
"This is sad, shameful and awful," said Imad Abumohr, a disabled rights activist, told reporters.
He said the Musalmeh case was shocking but not unheard of. He said last year they were called on to rescue a 17-year-old youth with mental disabilities who was thrown into a large rubbish bin.