The United States will seek the death penalty against Zacarias Moussaoui, the alleged "20th hijacker" in the Sept. 11 terror attacks that killed 3,000 people in New York and Washington.

Moussaoui, 33, a French citizen of Moroccan descent, is accused of conspiring with Usama bin Laden and the 19 hijackers to commit acts of terrorism, destroy aircraft, use airplanes as weapons of mass destruction and murder U.S. employees.

He is the only person to be charged in the Sept. 11 attacks. Four of the six counts brought against him carry a maximum sentence of death.

The government filed its announcement Thursday in Alexandria, Va., where Moussaoui's trial will begin Sept. 30. Prosecutors had until Friday to decide whether to seek the death penalty.

Attorney General John Ashcroft, who was in Miami, said the filing identified several "aggravating factors" that the government believed warranted execution. "Among these reasons is the impact of the crime on thousands of victims," he said.

"To that end we remain committed not only to carrying out justice but also to ensuring that the rights of the victims are fully protected."

Moussaoui's lead attorney, Frank Dunham Jr., said Ashcroft's announcing the death penalty filing was "disgraceful conduct" that could prevent selection of an impartial jury.

"We're trying to do this (select a jury) in the shadow of the Pentagon," said Dunham, federal public defender for eastern Virginia. "I am mystified as to why he feels he has to hold a televised press conference other than to influence the jury pool."

The decision to seek the death penalty is certain to have international implications, especially in Europe, where the terrorism investigation is continuing in several countries that oppose capital punishment.

Moussaoui's home country, France, asked Ashcroft recently not to seek the death penalty and noted that U.S.-French judicial agreements would exempt France from having to cooperate with U.S. authorities on the investigation if capital punishment is involved. France has long opposed the death penalty.

"We ask our counterparts in the international community to respect our sovereignty, and we respect theirs," Ashcroft said. "To the extent that they can cooperate and help us, we welcome that cooperation."

In its court filing seeking the death penalty Thursday, U.S. Attorney Paul J. McNulty said,  "The defendant, Zacarias Moussaoui, intentionally participated in an act contemplating that the life of a person would be taken or intending that lethal force would be used ... and the victims died as a direct result of the act." 

The document charged that Moussaoui engaged in an act of violence "knowing that the act created a grave risk of death to a person" and that "the crime constituted a reckless disregard for human life."

The government said it would seek to prove that Moussaoui committed the offenses "in an especially heinous, cruel and depraved manner in that they involved torture and serious physical abuse to the victims."

The offenses were committed "after substantial planning and premeditation to cause the death of a person and to commit an act of terrorism," the government argued.

Before his arrest, Moussaoui attended U.S. flight schools and "enjoyed the educational opportunities available in a free society, for the purpose of gaining specialized knowledge in flying an aircraft in order to kill as many American citizens as possible," the document said.

The government described the effects of the attacks as "the largest loss of life resulting from a criminal act in the history of the United States."

The government, describing the destruction caused when two of four hijacked jetliner crashed into the World Trade Center in New York, said the attacks caused the deaths of:

• 343 members of the New York City fire department, including the majority of its upper management and the loss of 92 pieces of equipment.

• 37 Port Authority police officers and 38 Port Authority civilian authorities;

• 23 New York City police officers.

The attacks also destroyed two major government law enforcement offices.

Prosecutors accused Moussaoui of some of the same activities as the Sept. 11 hijackers by taking flight training in the United States, inquiring about crop dusting and purchasing flight-deck training videos.

Moussaoui received money in July and August from Ramzi Bin al-Shibh, an alleged member of a German terrorist cell who was a roommate of Mohammed Atta, the suspected ringleader in the attacks, the indictment said. The FBI contends Bin al-Shibh may have been planning to be the 20th hijacker.

The indictment also alleged that Moussaoui attended an Al Qaeda camp in Afghanistan and by the end of September 2000 was making moves similar to some of the hijackers.

Prosecutors in northern Virginia first gave strong signals they considered this a capital case when they wrote March 7 to dozens of victims' families to say that, pending Ashcroft's final approval, "the United States will be asking the jury to find that defendant Moussaoui should be executed should he be found guilty."

The top prosecutors in the case have asked the families to tell their personal stories of grief and loss since the attacks. Authorities planned to interview family members of victims April 8 in Boston, where the two planes took off that struck the World Trade Center.

U.S. District Judge Leonie Brinkema already has denied a request by television networks to broadcast the Moussaoui trial, citing security concerns and a federal ban on cameras in federal courtrooms.

The Associated Press contributed to this report.