Mr Musa spoke after visiting his son, Imad, in a Jericho prison. Imad, 25, is one of nine men in their twenties and thirties from Al-Khader, near Bethlehem, who have been held by Palestinian military intelligence for a year on multiple-murder charges. They are alleged to have acted on orders from an Israeli secret service agent.
Palestinian human rights workers believe they were framed by a security apparatus running out of control. On 7 February Yasser Arafat's Justice Minister, Freih Abu-Medein, told the Palestinian parliament they were innocent and would be released within 48 hours. Three months later they are still behind bars. Their trial has been set for 22 June.
The Palestinian authorities now say they have all confessed. But the nine claim they were tortured until they signed false admissions.
Youssuf Musa accused their Palestinian interrogators of sexually abusing the prisoners, of threatening to settle accounts with their families, beating them and forcing them to drink sewage water. He last saw his son on Saturday.
"He told me they raped them with their batons," he said. "They tied their hands behind them and made them stand or sit naked in one position for hours at a time. They tied them to a rod and turned them like chickens on a spit. They hit them with electric cables."
According to Bassem Eid, director of the Palestinian Human Rights Monitoring Group, the Israeli army has admitted that two of the Al-Khader shootings were perpetrated by undercover Israeli soldiers.
One of the accused, Nabil Salah, 25, was serving a term in an Israeli prison when he was supposed to have murdered a man from his village on the way to the mosque. In another case, one of the supposed murder victims had committed suicide by drinking poison in front of her husband's family.
Mr Eid was presenting his independent group's first annual report at the end of a month in which two Arab land dealers were bludgeoned to death, apparently by Palestinian police, for selling land to Jews, and two Arab journalists have been arrested for doing their jobs.
"We are still," he said, "confronted with illegal detention, substandard prison conditions, lack of proper procedure and torture on a large scale."