Cuban spies who cooperate with the United States against their homeland are considered traitors worthy of being surveilled and confronted -- or worse, a former Cuban spy testified Wednesday.

Joseph Santos, an ex-spy and cooperating witness against five fellow Cubans on trial, said none of his Cuban trainers ever told him specifically what would happen if he switched sides and started working against Cuba's intelligence apparatus. Still, he was trained to expect ominous results.

``Perhaps a death sentence,'' Assistant U.S. Attorney David Buckner argued.

Before leaving Cuba for America in 1993, Santos said his fellow intelligence agents showed him a video that ``narrated the work that had been been done against a person that had committed treason, and it explained the surveillance carried out on that person.''

After Cuban agents determined what the man was doing, they ordered him to ``abandon those activities,'' Santos said. He wasn't told what ultimately happened to the man, but the message was clear.

``Were you told what would happen if you cooperated with U.S. law enforcement?'' prosecutor Buckner asked.

``That is not clearly explained, but at the national level, one knows what happens,'' Santos said. He did not elaborate.

The testimony took place outside the presence of jurors in the Cuban spy trial.

U.S. District Judge Joan Lenard rejected Buckner's argument that Santos faces a possible Cuban death sentence for his cooperation.

The judge said Santos has never faced a specific threat, so jurors should not hear him on the topic.

Prosecutors were trying to counter two days of cross-examination by the defense, which repeatedly hammered the point that Santos' plea agreement won him lesser charges and the probability of a sentence reduction.

They claimed that might have encouraged Santos to lie.

Santos and his wife, Amarylis, were originally arrested for conspiracy to commit espionage, which carries a maximum life sentence.

They ultimately pleaded guilty to a much lesser charge -- conspiracy to act as a foreign agent, which carries a maximum five-year sentence.

Santos was sentenced to four years on the government's recommendation.

``The fact is, in avoiding a life sentence [in the United States], he bought himself a death sentence'' from Cuba, Buckner argued about Santos.