Alexandria, Va. ? Rudy Giuliani made a powerful case Thursday for the execution of Zacarias Moussaoui, riveting the jury with horrific details of Sept. 11 as Moussaoui made fun of the catastrophe.

The former New York City mayor said he thinks every day of the couple who leapt to their deaths from the burning skyscraper while holding hands.

Moussaoui left court during a morning break singing a la Bruce Springsteen, “Burn in the U.S.A.!”

After convincing the 12 jurors to find Moussaoui eligible for execution for his ties to the Sept. 11 plot, prosecutors began the painstaking duty Thursday of telling the stories of those lost in the rubble that day.

Giuliani began what will be a wrenching few weeks of testimony by survivors and families of victims who are hoping to convince the jury to order Moussaoui killed by lethal injection.

The towers themselves rose again in the form of a 5-foot scale model on a table next to the witness stand. Giuliani motioned toward the 101st floor of the north tower, where he described seeing a man plummet from above the flames.

“I watched him hit right here,” Giuliani said, pointing to a spot at the foot of the buildings.

“I saw two people, who looked like they were holding hands. That’s the one that comes back to me every day,” he told jurors.

“Every day I think about it,” Giuliani said of the destruction at Ground Zero. “Horror, horror – the worst thing I’ve ever seen in my whole life.”

He narrated video of the planes hitting the towers, bodies falling, the buildings.

During his 2 1/2 hours on the stand, Giuliani ignored the smirking Moussaoui, even during Moussaoui’s outbursts. The former federal prosecutor kept his composure throughout his testimony, even as his narration brought audible sobs from the audience.

Part of his tale was raw and uncomfortable, while other parts were bittersweet remembrances.

Giuliani lovingly described close aide Beth Patrone Hatton, whose firefighter husband Terry died that day without knowing his wife was pregnant.

Giuliani said he had to identify Hatton’s crushed remains in a makeshift morgue and then break the news to Beth.

Moussaoui slouched silently during much of the testimony, but smirked when a prosecutor listed the lives and equipment the city, state and federal governments lost.

He waved his finger to track the trajectory of one hijacked plane shown in its final moments on TV screens.

He looked grotesquely pleased when victims leapt from the tallest floors.