A space scientist accused of attempted espionage was ordered held without bond Thursday after prosecutors said he was a "walking safe deposit box" of government secrets who claimed to have already passed some of them to Israel.

Magistrate Judge Deborah Robinson decided there was too much of a flight risk for Stewart Nozette, 52, of Chevy Chase, Md., to be free while he awaits trial.

Nozette pleaded not guilty to charges of attempted espionage, following his arrest last week. He is accused of seeking $2 million for selling secrets to an undercover FBI agent posing as an Israeli intelligence officer. The Justice Department could seek the death penalty.

Nozette had high-level security clearances during decades of government work on science and space projects. He was known primarily as a defense technologist who had worked on the Reagan-era Star Wars missile shield effort formally named the Strategic Defense Initiative.

Because he knows so many secrets, including about the nation's nuclear missile program, Attorney General Eric Holder has ordered special communications restrictions placed on him while he's in jail, authorities said.

"The defendant is himself a walking safe deposit box of classified information," said prosecutor Anthony Asuncion. "He is now a treasure trove of some of our most sensitive matters."

During the hearing, Asuncion played video excerpts of an undercover sting operation against Nozette in which the scientist lounges on a hotel room couch, discussing the possibility of having to flee the country if he comes under scrutiny from U.S. officials.

Nozette looked starkly different as he sat in court Thursday. Wearing baggy, black-and-white striped jail clothes, he stared passively as the screen showed him eating and laughing with the undercover agent.

Asuncion said Nozette told the agent he had passed classified information to Israel in the past. Nozette is not charged with doing so. Continued...