Story highlights

NEW: Pakistan's Supreme Court postpones a hearing for the nation's secretive spy agency

The ISI blames Abdul Saboor's death on natural causes

His mother says the 29-year-old was tortured and killed

The Supreme Court wants the ISI to explain the deaths and alleged detentions

(CNN) —  

Pakistan’s Supreme Court postponed a rare public hearing for the country’s secretive and powerful spy agency Thursday, a lawyer for one of the alleged victims of the agency said.

But the case breaks new ground in that the ISI has long been thought untouchable. Legal proceedings could expose the inner workings of the highly secretive agency like never before.

But attorney Tariq Asad told CNN the court had delayed the hearing until Friday because other proceedings took up much of the day.

Asad said it was clear the lawyer for the ISI, who was present when the postponement was announced, had not brought the seven detainees to court as ordered.

The spy agency’s lawyer presented the court with medical certificates for four of them to show they were hospitalized, and he asked permission from the court to present confidential letters explaining the whereabouts of the other three men, Asad said.

It’s not yet clear if the spy agency will produce the detainees at Friday’s hearing.

For Rohaifa Bibi, the proceedings are personal. Her son, Abdul Saboor, was one of the four men who died while in the custody of the ISI, the family claims.

“He had so many marks on his body,” Bibi said, pointing to numerous scars in a picture of her son’s corpse. “When they showed me the body, he was just skin and bones.”

The ISI blamed the 29-year-old’s death on natural causes. His mother said the scars prove the agency tortured and killed her son.

“It’s absolute lies,” Bibi said. “First, I read in the papers Abdul Saboor committed suicide, then they said he died of tuberculosis. When someone lies they should at least remember which lie they used.”

Her outrage has the 60-year-old doing what few others in Pakistan have ever dared think – taking on the ISI and demanding answers.

Those who know the ISI’s reputation know few people have ever challenged Pakistan’s most feared and shadowy institution. The spy agency has long been accused of backing and toppling politicians, using militant groups as proxies and backing extrajudicial killings.

The ISI has long denied the accusations, but no one from the agency ever speaks publicly on camera and no one from the ISI has ever been put on trial.

Because it has the backing of the Supreme Court, the case of Saboor could be different. The court has ordered the ISI to explain why Saboor, his two brothers and eight other men were arrested and why four of them died.

“We are fighting for the rule of law,” Asad said.

Saboor and his brothers made a living by printing Korans at a Lahore shop, Asad said. He said they were law-abiding but did acknowledge that all of the detainees were suspects in several militant attacks, though they were acquitted of the charges in 2010.

A lawyer for the ISI told the Supreme Court that the spy agency did detain the men for further questioning but said they were set free.

For Pakistan, the case is potentially a crucial test of the nation’s democracy. For a grieving mother, it’s a chance for justice.

“I can only hope that whoever has done this injustice to me, I hope their families suffer like I have,” Bibi said. “I hope one day they feel my pain.”

CNN’s Ed Payne and journalist Nasir Habib contributed to this report