Other Republicans on Specter's Judiciary Committee were divided over whether the Republican Bush administration's practices were satisfactory. Military officers and Justice Department officials defended the treatment of suspects at the detention center on a U.S. Navy base in Cuba's southeastern coast.
"We're holding them humanely," said Air Force Brig. Gen. Thomas L. Hemingway, a legal adviser to the Pentagon's Office of Military Commissions.
Attorney General Alberto Gonzales, in Belgium for talks with the European Union, defended the holding of prisoners at the Guantanamo Bay camp, estimating that about a dozen prisoners released from Guantanamo had been killed or captured later "on the battlefield."
"We can't release them and have them go back to fight against America," he told reporters in Brussels.
Critics — mostly human-rights groups and Democrats — long have accused the administration of unjustly detaining suspects at Guantanamo. Amnesty International recently compared the prison to Soviet-era gulags, and even some Republicans have questioned whether it should remain open.
The Senate panel convened to wade into the complicated system in place to detain, interrogate and, if warranted, prosecute foreigners suspected of having links to Afghanistan's former ruling Taliban militia or the al Qaeda terror network.
The administration calls the Guantanamo prisoners "enemy combatants," entitled to fewer legal protections that those afforded prisoners of war under the Geneva Conventions. Some detainees have been held for three years without charges.
The Supreme Court and lower federal courts have weighed in on detainees' rights but have issued conflicting opinions.
"It's a genuine crazy quilt to try to figure out where the due process rights lie," said Specter.
Military and Justice Department witnesses testified that extraordinary protections are in place for prisoners' rights and the processing of their cases. To ensure they weren't mistakenly classified as enemy combatants, each case goes through a process in which all evidence is looked at, and detainees get formal hearings before review panels, the officials said.