The Justice Department filed a 20-count criminal complaint against John Muhammad Tuesday, adding federal clout to the multistate effort to ensure that the Beltway Sniper suspect will be put to death if found guilty of his alleged crimes.

The government's complaint accuses Muhammad, 41, of using a firearm on multiple occasions that resulted in death, and of carrying out a deadly extortion plot, a violation of the Hobbs Act that can carry a death sentence.

Muhammad and John Lee Malvo, 17, are already charged with murder in Maryland and Virginia in the attacks that left 10 people dead and three others critically wounded. They are also charged with an Alabama slaying last month and are suspected in a February killing in Washington state.

The federal case could take precedence, though Attorney General John Ashcroft said negotiations over where the two men will first stand trial are continuing.

Muhammad was charged under the Hobbs Act, a 1946 union corruption law that allows the government to seek a death sentence against killers who try to extort money or disrupt interstate commerce. The charge was based on a note, found at the scene of one of the shootings, demanding $10 million.

However, Justice Department officials said prosecutors believe the firearms charges would make the best death penalty case at this point because they have the best evidence — a weapon linked to the killings.

"I believe the ultimate sanction ought to be available here," Ashcroft said, adding that the sniper slayings are "an atrocity."

Malvo was not charged in the 20-count criminal complaint, but he is identified as a John Doe in the supporting affidavit that describes some of the prosecution's evidence for the first time.

A judge must agree that Malvo can stand trial as an adult before he can be identified. The federal death penalty does not apply to juveniles, but Malvo could face the death penalty if he is convicted in Virginia or Alabama.

U.S. Attorney Paul McNulty of Virginia said it was undecided whether the government will move to the next step and obtain an indictment. But he said the complaint outlined "some of the grounds for a federal case."

The complaint names only seven victims — six killed in Montgomery County and a man gunned down in Washington, D.C.

A senior Justice Department official, speaking on condition of anonymity, said the Virginia cases were omitted because of that state's laws regarding double jeopardy — that is, being tried twice for the same crime. Federal charges covering those cases could be added later, the official said.

During an appearance in federal court here, Muhammad said, "Yes, sir," when asked if he understood the counts against him. Another hearing was set for Nov. 5.

Outside the courthouse, federal public defender Jim Wyda said Muhammad "stands accused of an incomprehensible crime, one that has had a profound impact on our community and has destroyed the lives of good people."

However, he said Muhammad has never been convicted of any other crimes, is innocent until proven guilty and has the right to a fair trial.

"What we're asking the public to do is respect that process. Mr. Muhammad needs it very badly," Wyda said. "This is a situation with so much emotion and so much passion, that it breeds the chance for errors, for mistakes."

Montgomery County prosecutor Douglas F. Gansler said government attorneys will have difficulty proving extortion was the motive for all the shootings.

"Most people have been operating under the idea [extortion] was an afterthought," he said.

The complaint charges Muhammad with affecting interstate commerce by extortion and threats of physical violence, interstate transportation in aid of racketeering, firing a gun near a school and other counts.

The accompanying affidavit details items found in a car that Muhammad and Malvo were sleeping in when they were arrested last week at a Maryland rest stop.

The items include a Bushmaster .223-caliber rifle police linked to most of the shootings and a glove stuck in a hole in the trunk. Authorities believe the sniper shot victims through the hole while lying in the trunk.

The glove matches one found at the scene of the Oct. 22 killing of a Maryland bus driver, according to the affidavit.

Also found was a Global Positioning System, a pair of two-way radios, a laptop computer and a wallet with several driver's licenses bearing Muhammad's photo but with different names.

The affidavit also confirmed that a tarot card with a note was found after the Oct. 7 shooting outside a school in Bowie. A second, longer note demanding $10 million was found after an Oct. 19 shooting in Ashland, Va. A handwriting analysis found they probably were written by the same person, according to the affidavit.

The longer note directed authorities to pay the $10 million into a credit card account or else "more persons, including children" would be killed, the affidavit says.

The credit card was stolen in Arizona in March and used a month later to pay for gasoline in Tacoma, Wash. — a former home of the two men and where police say the two are considered suspects in a Feb. 16 slaying.

Also Tuesday, a man arrested as a material witness in the case was flown from Michigan to Maryland, the U.S. Marshals Service said.

Nathaniel Osbourne, arrested Saturday in Flint, Mich., has been described by the FBI as a friend of Muhammad and co-owner of the car Muhammad and Malvo were captured in.

The Associated Press contributed to this report.