BOSTON -- A Cambridge couple who pleaded guilty to being secret agents for the Russian government, returned to Russia on Friday after an international spy swap in Vienna.

The switch took place in Vienna, the Justice Department said, with the United States transferring 10 Russian agents arrested in the U.S. on June 27 and the release by Russia of four people who had been imprisoned there.

"The exchange of these individuals ... has been completed," said the statement by Justice Department spokesman Dean Boyd.

Meanwhile, a Russian news agency said a plane carrying the 10 has landed in Moscow.

British media say the U.S. plane later brought the four Russians convicted of spying for the West to a U.K. military base in southern England.

Earlier at the airport in Vienna, two planes -- one from New York's La Guardia airport and another from Moscow -- had arrived within minutes of each other, parked nose-to-tail at a remote section on the tarmac, then spent about an hour and a half before departing just as quickly. A small bus was seen driving between the two planes.

Donald Howard Heathfield, 49, and Tracey Lee Ann Foley, 42, whose real names are Andrey Bezrukov and Elena Vavilova, were among those who appeared in federal court in New York. The couple was living in Cambridge with their two sons at the time of their arrests.

When asked if they knew they were committing a crime they both said, "Yes."

Last week, 11 people were arrested in what prosecutors said was a long-term Russian effort to infiltrate U.S. policy-making circles.

The group announced their pleas to conspiracy to act as an unregistered agent of a foreign country. An 11th defendant was a fugitive after he fled authorities in Cyprus following his release on bail.

During their appearance, the defendants provided little information about what kind of spying that they did for Russia.

"It's a resolution that will put this thing behind him as quickly as we can arrange it," said Peter Krupp, an attorney for Donald Heathfield, before the hearing.

Those who worked with and lived near the spies who posed as a Cambridge couple said they are still confused.

Foley, who was a licensed real estate agent, worked for a firm with offices in Somerville. She was described as extremely hardworking. Her supervisor said Foley's accent didn't sound Canadian but everything else checked out.

"It's not even something you can wrap your head around. We still wish her the best and wish the circumstances were different," said Alex Coon, of Red Fin Realty.

Foley and Heathfield lived near Harvard Square in a home they purchased last month for nearly $800,000.

The couple's children, Tim Foley, 20-year-old student at George Washington University, and 16-year-old Alex Foley, a student at International School of Boston, are reportedly already in Russia.