Moscow ? Russian authorities questioned crew members from the Arctic Sea cargo ship after the seamen and eight alleged pirates were returned to Moscow on Thursday, adding new details to the mystery of the ship’s monthlong odyssey.

Three heavy-lift air force jets, reportedly carrying 11 crew members, the alleged hijackers and other investigators, arrived at a Moscow region military base after flying from Cape Verde, the West African island nation where a Russian frigate stopped the ship four days ago.

State television channel Rossiya said the suspects claimed to be ecologists who had been arrested by mistake.

The saga of the Maltese-flagged freighter, which left Finland on July 21 carrying a load of timber to Algeria, has gripped much of Europe.

The ship was found nearly two weeks after it was to have docked in Algeria, thousands of miles off course and long out of radio contact.

Speculation on what was behind the freighter’s diversion was heightened by the involvement of the Russian navy, the slow trickle of information and claims that news media were fed bogus information about the ship.

It was unclear why three planes were needed to fly such a small group of people to Moscow, nor why Il-76s — among Russia’s largest planes — were used for the operation.

Federal investigators said in a statement that crew members told them that, while the Arctic Sea was in Swedish waters, the ship was boarded by eight men who wore uniforms that read “POLICE” on the back and who threatened the crew.

The statement did not give more details about the seizure or say if the men left the ship 12 hours later as earlier had been reported.

The Interfax news agency said the 11 crew members and hijackers were taken to Moscow’s Lefortovo prison, run by the main KGB successor agency. It cited an unidentified law enforcement official as saying the crew members will be freed if the investigators confirm they were not involved in the hijacking.

Rossiya said the alleged pirates identified themselves as ecologists when they were arrested. But in footage from the hold of one of the planes, a suspect identified as Andrei Lunev was asked what ecological organization he was connected with.

“I don’t know,” the man said. He also denied that he or the other suspects were armed.