Some 120 of the 400 stolen timekeepers were still missing, especially the more expensive models, Marcel Schlatter, press spokesman of the Zug police, told the sda news agency.
The watches had originally been stole in May 11 from the trunk of a car belonging to a 65-year-old salesman from the canton of Vaud. He had parked his car on a lot and left it briefly to run an errand.
When he returned to the locked vehicle, the watches in the trunk were gone.
Police won't speculate about the motive for the watches' return and they have no clues about the original thieves.
The watches are to be returned to their owner.