Gaining credible information from captured Al Qaeda operatives is tricky for government interrogators hoping to pry lose details that could prevent another attack.

Some of those who could be most helpful have repeatedly given investigators false information, law enforcement officials say. And many of the Al Qaeda members detained at the U.S. Naval Base in Guantanamo, Cuba, have remained silent for months.

But a senior law enforcement official said the United States has been able to use the detainees to generate solid leads by creating a network of information sharing between government agencies and the military.

Investigators use the network to put tips together like puzzle pieces, using information from U.S. Customs agents, the CIA, the military and intelligence agencies in other countries.

A random comment or mumbled name by a detainee can prove valuable when placed next to a document retrieved from Afghanistan or an intercepted call between suspected terrorists.

"Sometimes a tip will be used as the basis for a new round of questioning to those detained in Guantanamo," said a senior law enforcement official, speaking on condition of anonymity. "Sometimes, information from the interview is checked against other intelligence."

FBI spokesman Bill Carter said they "continue to receive information from detainees and from others about possible terror attacks. It is analyzed and disseminated so that agencies can take the appropriate action."

The method has led to some success in sifting through information from the United States' biggest catch in the war on terrorism -- senior Al Qaeda adviser Abu Zubaydah.

Authorities say Zubaydah identified Khalid Shaikh Mohammed as the operations planner for the Sept. 11 attacks on the World Trade Center and Pentagon. He also gave investigators vague information about an Al Qaeda plot to detonate a radioactive "dirty bomb" in the United States.

A memo, written by Defense Department adviser Michael H. Mobbs and released Tuesday by the Justice Department, revealed that Zubaydah later recanted his story.

It also highlighted the difficulty in separating fact from fiction.

Some of that information from two detainees has been corroborated, the memo says, but some "confidential sources have not been completely candid. ... Some information provided by the sources remains uncorroborated and may be part of an effort to mislead or confuse U.S. officials."

Law enforcement officials believe Zubaydah may have been trying to give only enough details to placate interrogators without foiling the plot.

But U.S. investigators checked the information against other intelligence and came up with the name of American Jose Padilla. He was arrested when he attempted to enter the United States at Chicago O'Hare International Airport in May and is being held by the military as an enemy combatant.

Other threats from Zubaydah have been publicized: He was the key source for the April threat to banks in the northeastern United States. In May, Zubaydah suggested New York monuments were a target.

The credibility of those warnings is still debated.

Some experts say gaining any useable information at all from Zubaydah is a success.

"It could be argued that this guy knows everything there is to know about Al Qaeda," said Justin Williamson, a former FBI analyst. "We've had him for a long time and eventually he'll begin to leak good intelligence, interspersed with disinformation. Getting anything out of him will be difficult because he'll probably be willing to go to his grave before he gives up major details of Al Qaeda operations."

Other pointed to the numerous terror warnings and alerts, which officials have said were based in part on interviews with Guantanamo detainees, as an indicator that the interrogations have not been successful.

"Where is the hard data that allows the (government) to break up major attack plans?" said Vanessa Thompson, a researcher who studies law enforcement interrogations at the University of New Mexico.

"It seems as though every time they get someone down there to talk, the government puts out an alert and nothing happens. I think all we're getting is a lot of disinformation."