In Vienna on Friday, U.S. marshals turned over the 10 Russian sleeper agents in exchange for four Russians convicted of spying for the U.S. and Britain.
The attorney general says swapping the agents offered the chance to get back four people "in whom we have a great deal of interest."
Holder also sought to erase concern over the fate of the children of the Russian agents, saying they all were allowed to return to Russia "consistent with their parents' wishes" or, in the case of those who were adults or nearly adults, were allowed to make their own choices of where to live.
An 11th suspect, who jumped bail last week after being arrested in Cyprus, remains on the loose.
The defendants were accused of living seemingly ordinary lives in America while they acted as unregistered agents for the Russian government, sending secret messages and carrying out orders they received from their Russian contacts.
The Associated Press contributed to this story.