Ten other suspects - all arrested in the U.S. - remain in jail. The case comes after a decade-long investigation in which the government has yet to reveal why the probe began or why it ended when it did.
In the New York City community of Brighton Beach, home to one of the largest Russian populations outside Russia, this week's arrests of 11 alleged Russian agents came as no surprise, CBS News Correspondent Elaine Quijano reports.
"I believe they have spies here 100 percent," said one New Yorker. "You know, this country is a little naive."
The 11 have not been charged with actual spying. Instead, prosecutors have charged them with conspiracy to act as unregistered agents of a foreign government.
"It's possible that they never actually caught them in the act of committing espionage," Charles Pinck, president of The Georgetown Group, said.
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The FBI had the suspects under surveillance for nearly a decade, monitoring all of the places they lived and many of the places where they met, including hotels, diners, coffee shops, even a Manhattan subway station. That surveillance continued until just last week when one suspect met with an undercover FBI agent.
Prosecutors say suspect Anna Chapman was asked by the agent, who was posing as a Russian consulate employee, if she would pass along a document to another Russian.
"Are you ready for this step?" the FBI agent asked, according to court documents.
"[Expletive], of course," Chapman allegedly replied.
Court documents reveal that in 2004 a suspect known as "Christopher Metsos," who prosecutors say was an overseas-based Russian agent, buried some cash in upstate New York. Two years later, suspects who went by the names "Michael Zottoli" and "Patricia Mills" dug it up, and the FBI says it caught the whole thing on tape.
The big question: what was the alleged network's ultimate mission?
"They were sent to Washington, the center of political power, to New York, the center of financial power, and to Boston, with Harvard and MIT really the center of educational power," Pinck said.
"This was an investment of time, money, training those people," Peter Earnest, executive director of the International Spy Museum in Washington.
Earnest is a 36-year-veteran of the CIA. The suspects may have been acting as so-called "spotters" for Russian intelligence, he said.
"One of the things they can do is keep an eye out and assess people who might be recruitment targets then you bring in a hard-core intelligence officer who attempts to recruit that individual," Earnest said.
A serious case, experts say, in which the lack of details has deepened the mystery.