The security officials who arrested Haytham Amr in June said they only wanted to "borrow him" for questioning about his ties to the Islamist Hamas movement, Amr's father said.

Three days later, the 33-year-old nurse was dead from internal injuries, and the initial explanation from officials -- that he had jumped from a window to escape -- quickly gave way to a broader reckoning about the treatment of detainees in Palestinian facilities. There have been at least four deaths this year that human rights groups say may be linked to mistreatment in detention facilities run by the Palestinian Authority in the West Bank, and at least three in facilities in the Hamas-ruled Gaza Strip.

The two factions are involved in a long-standing struggle for control of Palestinian society, a fight with profound implications for the future of the U.S.-sponsored peace process. The Palestinian Authority favors negotiations with Israel; Hamas's founding charter calls for its elimination. Over the years their battle has played out at every level, from elections to vicious gunfights. In Amr's case, it was set in the depths of a Hebron detention cell.

The prison deaths pose a particular challenge for the U.S.-backed administration of Palestinian Authority President Mahmoud Abbas and Prime Minister Salam Fayyad, who must show they can maintain security to the satisfaction of the Israelis without resorting to methods that erode their political standing in the West Bank.

"You can't isolate these incidents from the environment and atmosphere of our country," where a violent intifada, or uprising, against Israel gave way to factional fighting between Hamas and the rival Fatah, the dominant party in the West Bank and within the Palestinian Authority, said recently appointed Palestinian Authority Interior Minister Said Abu Ali.

His first months on the job have included a focus on trying to curb the mistreatment of West Bank prisoners. Hamas took control of the Gaza Strip two years ago, and operates its own government there.

A U.N. Human Rights Council report released this week accused Israel and Hamas of war crimes during the three-week war in Gaza last winter, and also criticized what it characterized as widespread human rights abuses by both Hamas and Fatah -- from political arrests and extrajudicial killings to mistreatment of detainees. The report, by South African judge Richard Goldstone, also noted the thousands of Palestinian prisoners held in Israeli jails.

While U.S.- and European-backed security forces and police have helped restore basic order in West Bank cities, Abu Ali said, the Palestinian criminal justice and intelligence services now need similar reforms -- to make the rules of operation and the lines of command clear. In August, he issued a directive forbidding "physical or psychological punishment," ordering medical care for those who need it and holding commanders responsible.

The Amr case "will be set as an example," he said in an interview. "There is no doubt there was an excessive amount of force used in interrogation."

He said that a military court is investigating and that about 15 people had been temporarily removed from duty in Palestinian intelligence and other services until the probe is complete. He said he expects charges to be brought against those directly responsible for Amr's death and permanent changes to be made in the command of the Hebron area intelligence service.

Human rights groups are hesitant to offer too much hope for change. It has been long-standing practice, they say, for prisoners in Palestinian-run facilities -- particularly inmates who are considered political detainees -- to be beaten on the soles of their feet, strapped into painful positions and subjected to other forms of abuse. Such methods, they argue, may prove hard to curb.

The death in custody last year of popular Hamas cleric Majd Barghouti drew similar calls for reform after an independent investigation found that he was badly beaten during interrogation in a facility in Ramallah. The official explanation at the time was that he died of a heart attack.

"People are paying a very heavy price" for the conflict between Hamas and Fatah, said Hamdi Shaqqura, a researcher with the Gaza-based Palestinian Center for Human Rights. "No one is ever brought to justice. No punishment is applied. It's an environment for more people to die."

But others note an unexpected openness in the investigation of Amr's death and in the probe of another fatal incident, in which Fadi Hamadneh, a detainee in the Junaid facility in Nablus was found hanging from a pipe.

Hamadneh's death was ruled a suicide by Palestinian Authority officials. Family members asked for an independent autopsy, and the authority allowed the Ramallah-based human rights group Al-Haq to have a visiting Danish forensic scientist perform it.

That investigation concluded that Hamadneh hanged himself -- though both the family and Al-Haq question whether mistreatment in the facility may have prompted the suicide. Still, the fact that an independent autopsy was allowed, coupled with the expected charges in the Amr case, may signal the start of more accountability for a detention system that's been regarded as a blot on Palestinian self-governance.

"It has been happening for a long time, but it has intensified because of political reasons, the tension between the two sides," said Shawan Jabarin, general director of Al-Haq.

Jabarin said his organization and others are watching the Amr case carefully to see if it represents a turning point.

Like many of the hundreds of Hamas members arrested in the West Bank, said Interior Minister Abu Ali, Amr was suspected of links to an armed cell of the Islamist movement. Palestinian Authority security and intelligence forces have been trying for the past two years to root out such cells, fearful of an armed challenge to Abbas's government.

But Amr's father and extended family are closely allied with Fatah, and have been pressing hard for action against those responsible. Abdullah Amr, 66, said his son, who left behind three children of his own, was sympathetic to the views of Hamas but was not active in the organization and did not break any laws. He said his son was well liked in the community for his work at a local health clinic.

"My son was taken from my lap to be executed," said Amr, who described himself as a 40-year Fatah loyalist. "The Palestinian Authority knows who killed my son, and the Palestinian Authority should apply justice."