If foreign agents spy, why not charge them with espionage?

The sensational FBI arrests of 10 people in the United States for allegedly spying for Russia raise the question: If the suspects supposedly spied, why not charge them with espionage?

Winning a conviction for espionage requires proof that a defendant passed classified information to a foreign government, and it doesn't appear from court papers released so far that any of the 10 people even had access to government secrets, much less passed them on to Moscow.

On the other hand, it's possible the FBI acquired evidence of espionage, but may have compelling reasons for not disclosing it.

Among them: Exposing the details of how the FBI gathers evidence could hurt the ability of law enforcement to gather it in the future.

"There are very sensitive means of collection in the counterespionage realm" and the government "may have made a decision based on having to try a case in an open courtroom," said McGregor Scott, a former U.S. attorney for the Eastern District of California.

Instead of espionage, the defendants are charged with conspiracy to act as agents of a foreign government while concealing that from the U.S. government — a much easier case to prove. A second conspiracy charge of money laundering is based on payments to the defendants that allegedly originated at the headquarters of Russian intelligence.

This is hardly the first time suspected spies have been charged with something besides espionage. Mishandling classified information is one alternative to charging espionage when, for example, investigators have proof that someone removed classified information from government files, but are unable to show that they gave it to a foreign power.