Three accused Russian spies now in custody, and another man still at large, posed as Canadians to cover their tracks while on "deep-cover" assignments in the United States, the U.S. Justice Department says.

The three were among 10 arrested as alleged agents of Russia's intelligence service, the department said in a release.

The defendants known as Donald Howard Heathfield and Tracey Lee Ann Foley claimed to be born in Canada, while Patricia Mills claimed to be a Canadian citizen, court papers filed in the U.S. District Court for the Southern District of New York showed. The FBI is still looking for Christopher Metsos, who also claimed to be a Canadian citizen.

Heathfield and Foley, a married couple, lived near Boston. In searching a safe-deposit box in Cambridge, Mass., investigators found a photocopy of a birth certificate in the name of Donald Howard Graham Heathfield, a Canadian infant who died many years ago.

Corporate websites described Heathfield as developer of Future Map, a software system, and as a principal with the Massachusetts office of Global Partners Inc. His resumé said he has a bachelor of arts degree in international economics from Toronto's York University.

Court documents said Foley travelled on a fake British passport prepared for her by the SVR, the foreign intelligence arm of the Russian Federation.

A real estate website said she is a Montreal native educated in Canada, Switzerland and France. It said Foley once worked as a human resources officer in Toronto and ran her own travel agency in Cambridge, Mass., that specialized in organizing trips to French wine regions for small groups of enthusiasts.

The FBI said Moscow instructed the couple to gather information on U.S. foreign policy in such areas as use of the internet by terrorists, the military and Central Asia. In one instance, Heathfield supposedly told Russian spymasters he had made contact with a U.S. nuclear weapons researcher.

Secret messages

The FBI alleged Heathfield and Foley communicated with Moscow headquarters through special computer software that embeds secret messages in images — a process known as steganography.

Mills and her co-defendant husband, Michael Zottoli, lived for years in Seattle before moving to Arlington, Va., last October.

The FBI said Metsos does not live in the U.S., but it didn't disclose his country of residence, only that he often travelled to the U.S. to meet with agents and pay them on behalf of Moscow.

In 2004, a Russian government official surreptitiously handed Metsos money in New York, the documents alleged. Metsos then buried some cash in upstate New York and, two years later, Mills and Zottoli flew there and dug it up, the FBI said.

Lengthy probe

The case was the result of a multi-year investigation by the FBI, the U.S. Attorney’s Office for the Southern District of New York and the U.S. Justice Department.

The FBI alleged that the defendants were living and operating in the U.S. with the long-term goal of becoming sufficiently "Americanized" that "they could gather information about the United States for Russia" and could "successfully recruit" sources who are able "to infiltrate United States policy-making circles."

"This is something right out of the Cold War days from the '50s and '60s," said Fred Burton, a former special agent with the U.S. State Department who is a security expert at Austin, Texas-based Stratfor.

He said it's a textbook Russian intelligence operation.

"They like third-country operations," he said, adding that the most obvious choices for operations running against the United States are Mexico and Canada.

All 10 people face charges of conspiracy to act as unregistered agents of a foreign government without notifying the U.S. government, and they could face five years in prison if convicted.

All but two were charged with conspiracy to commit money laundering, which carries a maximum penalty of 20 years in prison.