Family members of those who died at the hands of terrorists aboard a hijacked aircraft on Sept. 11 listened to a chilling recording of their loved ones' final 30 minutes today, leaving, for the most part, less devastated than before and in some cases with their spirits lifted.

"These were clearly people who were unafraid of the unthinkable," said Hamilton Peterson, whose father, Donald A. Peterson, died when the plane crashed in rural southwestern Pennsylvania. "They digested it and acted upon it in no time at all."

Some said the cockpit voice recording of United Airlines Flight 93 confirmed their beliefs that many passengers had attacked their hijackers with great force, in an attempt to retake control of the plane.

"A lot of [the tape] was unintelligible, and a lot of it we couldn't follow very easily, so I don't think it gives us resolution," said Tom Burnett, 72. His son, Tom Jr., had intimated in a series of cell phone calls to his wife during the flight that he and fellow passengers were organizing a revolt. "I'm content with what happened [on the plane]. I felt that I learned something, another piece of the puzzle."

The FBI played the cockpit recordings for family members of the crew this morning and separately revealed them to passenger families this afternoon. It was the first time such tapes had been played for families of victims of a U.S. airplane crash.

The decision to play the tape for persons other than investigators prompted some criticism from pilots and aviation experts, who said it could set a dangerous precedent in the use of future recordings.

Flight 93 was headed from Newark to San Francisco when it crashed, killing 40 passengers and crew and four presumed hijackers on board. The passengers and crew have been heralded as heroes ever since for preventing what is believed to have been a fourth suicide terror attack, possibly on Washington.

Only family members and FBI officials were allowed in the Marriott hotel conference room where the tape was played, and no printed transcripts of the tape were distributed. Members of the media were prohibited from entering the hotel.

Four family members per victim were allowed to listen to the tape twice and ask questions of FBI agents who are familiar with its contents. Grief counselors were on hand to help family members.

They listened to the tape on headphones as transcripts were projected onto a screen. They described the room as "somber" and "intense." A few people who came to hear the recording left before they could do so.

The FBI asked the people who listened not to discuss details with the media. As a result, many of the lingering questions, including whether the passengers intent on storming the cockpit retook control of the aircraft, will remain unanswered for now.

Relatives said much of the tape is chaotic, with shouting and clear indications of violence.

"Listening to the last 30 minutes of your loved one's life is emotional," said Mary Jurgens, Tom Burnett Jr.'s sister. "It took a lot of time listening to those 30 minutes. It felt like hours."

For Deena Burnett, the recording offered a chance to hear for herself the final moments of her husband's life. For Kimi Beaven, it was an opportunity to sort fact from conjecture. For others, it was emotional closure, a way both to experience their loved ones' terror and to begin leaving the awful events of Sept. 11 behind.

"It's too important to rely on someone else's translation of what they think happened," Burnett, 38, said before listening to the recording. "This is the only tangible information that we as family members have."

FBI officials initially said they would not permit family members to listen to the tape, but FBI Director Robert S. Mueller III granted them access in March.

Several relatives had been lobbying to hear the tape since shortly after Sept. 11, and in some cases threatened lawsuits. The strong likelihood that the tape will be played publicly during the government's prosecution of alleged hijacking conspirator Zacarias Moussaoui influenced the FBI's changed position, sources said.

Attorney General John D. Ashcroft said today that the Princeton meetings were part of "an unprecedented effort to reach out to and work with the families of victims and surviving victims of September 11 and include them in the process of justice."

In addition to listening to the audiotape, family members in Princeton participated in interviews with federal prosecutors and FBI agents to document the suffering caused by the Sept. 11 attacks.

The U.S. government plans to use family testimonials to argue in favor of the death penalty if Moussaoui is convicted.

Burnett, 38, the mother of three daughters, said she wanted to understand better how the plane went down.

She said her husband, chief operating officer for a medical device company, called her on his cell phone four times during the flight. Each call was progressively more urgent, she said, as she relayed details of other hijackings to him and he intimated to her that he and several other passengers were planning to "do something" to stop the hijackers.

"I know that he was capable of handling the situation," she said. "When that plane crashed, I knew that something had gone wrong" with his plan.

Tom Burnett Jr. and three other passengers -- Todd Beamer, Honor Elizabeth Wainio and Jeremy Glick -- along with two flight attendants, reported in cell phone calls that passengers advanced down the plane's aisle toward the cockpit. In news accounts of the cockpit voice recording and conversations with air traffic controllers, it has remained unclear whether the passengers entered the cockpit.

Other family members said they simply needed to know what the cockpit voice recorder had picked up.

"We didn't want to hear it in the media," said Carole O'Hare, 49, whose mother, Hilda Marcin, died in the crash. "That's how we found out Mom's plane crashed, and I didn't want to hear it that way again."

Beaven, 34, whose husband, Alan, was on the flight, said she came to hear the tapes to "experience just a glimpse of what he went through."

"Every hard time I ever went through, he was with me, so somehow it makes me feel that I can be with him for a short time," she said.

Chris Beaven, left, and brother John enter a Princeton, N.J., hotel to hear the cockpit recording of Flight 93. Their father, Alan, died in the crash, and his wife said she wanted to "experience just a glimpse of what he went through."