The Baseball Stars

well my wife got a present at her office and it was a signed baseball...
the receptionist said he left it on her desk after hours.
(there are janitors that clean the office)
the box was there the next morning and so was the card but the gift.............WAS GONE!!!
who was stealing (did the butler do it?)
how should we set up a sting to catch the thief?
i don't want to get anymore things stolen
how should i catch them in the act? i think it's the cleaning crew too but how should i trap them?
and yes other people's stuff had been stolen as well. the stolen stuff was a lot more valuable then a baseball; laptops and brief cases were stolen too!