The stories and photos of four young children, all of whom lost parents in the 9/11 attacks, brought witnesses to tears and visibly affected jurors Thursday at the death penalty trial of Al Qaeda conspirator Zacarias Moussaoui.

The second phase of the sentencing trial — to determine whether Moussaoui deserves execution or life in prison — opened Thursday. Early on, prosecutors played videos of the two hijacked jetliners hitting the gleaming World Trade Center towers. They also showed videos of people plunging more than 80 stories to their deaths and punctuated their presentation with family photos of loved ones.

Each hour the emotional impact grew.

Former New York Mayor Rudolph Guiliani retold the now-familiar tale of his own harrowing experience in debris-choked lower Manhattan on Sept. 11, 2001. But it was not until he spoke of the daughter of one of his closest aides, Beth Petrone Hatton, that Guiliani's voice quaked and broke. Firefighter Terence S. Hatton — who earned 19 medals in 21 years — died without knowing his wife was pregnant.

One female juror looked stricken. The rest hung motionless on Guiliani's every word.

Even Moussaoui, who had affected a look of boredom during the showing of video of falling bodies, watched the ex-mayor intently as he described Terry Hatton, who was born May 15, 2002. Her picture with Guiliani flashed on the screen.

"Terry's going to grow up without a father ... without a very special father," Guiliani said. "You can't replace that. ... There's no way that money, camps and scholarships, which is very important and which we raised, can replace that." Guiliani aides in the audience dabbed their eyes with tissue and sniffled.

Then came retired firefighter Anthony Sanseviro, whose co-worker and friend Danny Suhr died after he was hit by a body falling from one of the towers: "It was like a missile coming in."

As a photo was shown of Suhr with his daughter, Briana, Sanseviro described how Suhr's wife and childhood sweetheart, Nancy, has struggled to bring her up without him.

He was followed to the stand by James Smith, a 21-year veteran of the New York Police Department with a 6-year-old daughter, Patricia. His wife, Moira, also a police officer, was bringing a woman with asthma down from the third floor of the South Tower when it collapsed on them.

"Moira was a gung-ho police officer, who took chances and made a lot of arrests, until Patricia was born," he said. "She went from street narcotics to community policing. She decided that she wanted to be a mother even more than a police officer."

Asked to describe the loss felt by his daughter, Smith replied in a quavering voice: "The loss to Pat ... I can't begin to describe ... all the things she'll never be able to do with her mother, the first day of school, the relationship with her mother ..."

He stopped for a drink of water.

Prosecutor David Raskin showed a photo of Patricia taken Dec. 4, 2001, and asked Smith to explain it.

It showed a girl, 2 1/2, with long dark hair in a red dress that flowed to her ankles. She was wearing a long blue ribbon looped around her neck and attached to an object below her knees.

"That was Valor Day, when the New York Police Department hands out medals," Smith said. "She's wearing the medal they awarded Moira, the department's highest honor, the Medal of Honor."

The stricken-looking female juror pulled a tissue out and wiped her eyes. A male juror nearby appeared to be on the verge of tears. The burly, balding cop also wiped his eyes.

An Nguyen was 4 when his father, Khang Nguyen, was killed at the Pentagon. Prosecutors showed a picture of the boy at the Pentagon gates a few days after the attack, looking for his dad.

"He became heartbroken, quiet," said An's mother, Tu Nguyen. "He didn't have enough words to express his feelings."

When his dad was in heaven, An decided that he wanted to become an astronaut, "so he can go into space and look for his daddy," she told the jury.

Later, jurors heard the voice of lead hijacker Mohammed Atta aboard the jet that hit the first tower in New York. In a broadcast intended for passengers but mistakenly transmitted to air controllers, Atta said, "We have some planes. Just be quiet and you'll be OK."

The brother-in-law of a Sept. 11 victim testified that his sister committed suicide a month after her husband, Vamsi Pendyala, was killed on the plane Atta hijacked. Chandra Kalahasthi read to the jury the suicide note written by his sister, Prasanna: "I want to be with my loving hubby."

Leaving court at day's end minutes later, Moussaoui shouted, "No pain, no gain, America."

Prosecutor Rob Spencer braced jurors for the painful testimony they were going to hear over the next few weeks. The voices of the victims of the attacks and their anguished families should be all jurors need to hear to conclude that Moussaoui should die for his crimes, Spencer said.

Spencer described one call from a woman on the 83rd floor of the second tower to fall. "The floor is completely engulfed," she said. "We're on the floor and we can't breathe.... I don't see any more air. ... I'm going to die, aren't I?" The tape apparently will be played later.

Prosecutors also will play the cockpit recordings from United Flight 93, which crashed into a Pennsylvania field on Sept. 11, after passengers fought back against the hijackers. The tape has never been heard publicly.

"You cannot understand the magnitude of that day unless you hear it from the victims themselves," Spencer said. Moussaoui smiled several times when the prosecution mentioned his enthusiasm for the attacks.

Defense lawyer Gerald Zerkin said both Moussaoui's sisters are paranoid schizophrenics and his father is very troubled and may be schizophrenic as well. Noting the disease is inherited, Zerkin plans to call a doctor who believes Moussaoui suffers from a mentally illness that probably is schizophrenia.

Zerkin acknowledged that testimony about the impact on victims will be overwhelming. He urged jurors to "somehow maintain your equilibrium. ... You must nevertheless open yourselves to the possibility of a sentence other than death."

Zerkin described how Moussaoui grew up with little religious training and fell under the influence of radical Muslims when he traveled to London in hopes of becoming a businessman.

Spencer countered: "It was his choice to become a terrorist and it was a choice he was proud of."

Moussaoui, 37, is the only person charged in this country in the Sept. 11 attacks. He pleaded guilty last April. On Monday, the jury decided he was directly responsible for at least one death on 9/11 and is eligible for execution.

Moussaoui was in a Minnesota jail on Sept. 11. Nevertheless, the jury concluded that he could have thwarted or minimized the attacks if he had confessed his Al Qaeda membership and terrorist plans when federal agents arrested him in August 2001 while he was taking flight training.