Seventeen-year-old sniper suspect John Lee Malvo can be tried as an adult, making him eligible to receive the death penalty, a judge ruled Wednesday.

"There is no eyewitness at any of the four crime scenes but the circumstantial evidence is quite strong," Juvenile Court Judge Charles Maxfield said.

Maxfield made his decision after a hearing in which prosecutors said Malvo tried to extort $10 million from authorities during the killing spree and that fingerprints on the murder weapon and other evidence tied the teen-ager to four attacks, three of them fatal.

Malvo and John Allen Muhammad, 42, are accused of killing 13 people and wounding five others in Alabama, Georgia, Louisiana, Maryland, Virginia and Washington, D.C., last year. They are being tried first in Virginia in separate trials.

The extortion allegation is a key element of a Virginia anti-terrorism law that allows the death penalty for killers convicted of trying to intimidate the public or coerce the government. Malvo is also charged under a statute that allows a death sentence for multiple murders.

"They wanted to negotiate for money," prosecutor Robert F. Horan said. "They said 'If you want us to stop killing people give us the money.' If that is not intent to intimidate government, I don't know what is."

Defense lawyers argued the evidence was insufficient because no eyewitnesses placed Malvo at any of the crime scenes. They also said the demand for money does not qualify as terrorism and questioned whether it should be interpreted as a motive for any alleged crime.

"This is not intimidation if you look at it. If you look at it in the broadest sense, it's blackmail," defense lawyer Michael Arif said.

After the hearing, he added: "The request for $10 million sounds like something out of an Austin Powers movie."

Malvo is charged in Fairfax County with the Oct. 14 slaying of FBI analyst Linda Franklin outside a Home Depot store in Falls Church. But Horan said ballistics evidence, the notes and the phone calls link Malvo to two other fatal attacks and a shooting outside an Ashland restaurant that left a patron critically wounded.

A fingerprint expert also said the only identifiable prints found on the murder weapon, a Bushmaster rifle, belonged to Malvo. The print was found on the rifle's pistol grip.

Earlier, a detective who interviewed Malvo for six hours after his arrest last fall identified his voice on tape recordings of two threatening phone calls to authorities during the attacks. Both tapes were played in court.

"I talked to him long enough to know he's very smooth and well-spoken. I'd know that voice immediately," Fairfax County police Detective June Boyle testified. She described Malvo as calm, relaxed and even "jovial on occasion" during their interview last year.

Defense lawyers challenged whether the caller was even male. Boyle conceded she had no special training in voice identification but the judge ruled her testimony was admissible.

One of the calls, made Oct. 21, was monitored by FBI agent Jackie Dalrymple. She said someone claiming to be a sniper laid out non-negotiable terms for ending the killing spree.

The caller ordered police to hold a news conference and say they believed they had caught the sniper "like a duck in a noose." Otherwise, the caller told police, "be sure to know that we will not deviate" from previous threats to kill more people.

Other testimony focused on a note found Oct. 22 near the Silver Spring, Md., location where bus driver Conrad Johnson was slain. The note read: "For you Mr. police, call me God. Do not release to the press. Can you hear us now! Do not play these childish games with us. You know our demands."

According to Horan, the note also said Johnson was killed because police hadn't responded quickly enough to earlier demands for money, telling police: "Your incompetence has cost you another life."

Prosecutors said they will take their case against Malvo to a grand jury Tuesday and hope to bring the case to trial this summer. After the hearing, defense lawyers said that court papers, which in juvenile court are sealed, indicate that Malvo's name is actually Lee Boyd Malvo.

Muhammad faces trial in October in neighboring Prince William County for the Oct. 9 slaying of Dean Meyers at a Manassas gas station.

The Associated Press contributed to this report.