Police had stored 28.6 kilograms of hash and 4.8 kilograms of pot, seized from three different investigations, in a building in Châtillon, near the city of Fribourg.
The drugs were likely stolen in late November or early December last year but the theft was only recently noticed, according to media reports.
Cantonal police said they discovered that a metal bar on one of the windows at the rear of the warehouse had been sawn off on December 5th, the Fribourg newspaper La Liberté reported online on Tuesday.
At the time police believed that whoever was responsible for removing the bar would not be able to penetrate inside the building, the newspaper said.
The police employee in charge of managing confiscated items, who was on sick leave for several months before returning to work in February, noticed that objects had been removed, police said in a news release.
But it was only on March 13th that he noticed the drugs were missing when he sought them out for a planned analysis of the substances.
At the time of the break-in, the warehouse alarm system was not turned on for “technical reasons”, La Liberté reported without giving further details.
A police investigation is under way to find out exactly what happened.
The news about the break-in emerged as cantonal police issued a press release this week about an increase in burglaries for 2012, with 14,674 cases recorded in Fribourg last year, up 9.1 percent from the previous year.