LISBON, Portugal (AP) — Portugal's attorney general's office says authorities have detained military police investigators and members of the country's paramilitary National Republican Guard in connection with last year's theft of weapons from the national armory.

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.