A statement Tuesday said public prosecutors are investigating how the stolen weapons reappeared four months later in a field about 30 kilometers (20 miles) away, where they were recovered after an anonymous tip-off.
It says those taken into detention are suspected of criminal association, forgery and arms trafficking, among other crimes. The statement gave few details because a judicial secrecy law forbids the release of information about open investigations.
At the time of the June 2017 theft, the defense ministry said it was a "very professional" job. Nobody has been charged in connection with the robbery.