One boy wanted to become an astronaut so he could go into space and find his daddy in heaven. One girl lost her father, a hero firefighter, before she was even born.

The tales of pain and devastation wrought by the Sept. 11, 2001, attacks were told Thursday as prosecutors opened the second phase of their death-penalty case against Zacarias Moussaoui. Dozens of equally painful tales are expected as the trial continues.

In this second phase of the trial, prosecutors are seeking to prove Moussaoui deserves execution by highlighting the personal toll inflicted on so many on Sept. 11.

Moussaoui, the only person in this country charged in the Sept. 11 attacks, was found eligible for the death penalty Monday when a jury concluded that he directly caused at least one of the deaths on that day.

Courtroom observers and some jurors were shaken as they heard some of the victim-impact testimony.

An Nguyen was 4 years old when his father, Khang Nguyen, was killed at the Pentagon. Prosecutors showed a picture of An standing 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 An was told his dad was in heaven, An decided he wanted to become an astronaut, "so he can go into space and look for his daddy," she told the jury.

Moussaoui made light of the testimony he heard.

"No pain, no gain, America," he said at the end of Thursday's hearing.

The government's first witness, former New York Mayor Rudolph Giuliani, became choked up when he described how his longtime secretary Beth Petrone Hatton lost her husband, firefighter Terence S. Hatton, in the attacks.

A few days after Terence Hatton died, Beth Hatton learned that she was pregnant with the couple's first child.

Emotions increased when a picture of the baby girl, born in May 2002, flashed on courtroom screens.

"Terry's going to grow up without a father ... without a very special father," Giuliani said. "You can't replace that."

Jurors saw videotapes of two hijacked jetliners hitting the World Trade Center and watched people jump to their deaths from some of the top floors of the 110-floor skyscrapers to avoid being burned alive.

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."

Defense lawyers, in their opening statement to the jury, urged them to "somehow maintain your equilibrium" in the midst of emotionally devastating testimony.

"You must nevertheless open yourselves to the possibility of a sentence other than death," defense lawyer Gerald Zerkin said.

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 mental illness that probably is schizophrenia.

It was indeed hard to maintain equilibrium during Thursday's hearing. One firefighter described how his friend and mentor died after he was hit by a falling body from one of the twin towers.

Another man described how his sister committed suicide a month after the attacks, grieving over her husband's death on American Airlines Flight 11, the first plane to hit the World Trade Center.

Chandra Kalahasthi read to the jury the suicide note written by his sister, Prasanna: "I want to be with my loving hubby."

One woman who shot video of the attack from her hotel described hearing "audio fireflies" — a chirping that she later learned is emitted from firefighters' equipment when they are motionless for extended periods of time.

In his opening statement to the jury, 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 said about 45 victim-impact witnesses will be called to testify, representing less than 2 percent of the nearly 3,000 people who died on Sept. 11.