Theft, although not considered a serious crime under the Criminal Code, causes not only direct material damage (sometimes very large!) To the victim, but also severe mental trauma. It is very unpleasant to realize that some mean person has climbed into your house, into your pocket, into a locker or a desk drawer at your workplace. The desire is quite natural: to find and punish the bastard! But how to do that?
If the theft is committed at work, then a lot depends on the procedures established there. For example, in the case of a “walk-through yard”, when both employees and casual visitors rush back and forth, the chances of finding a thief, alas, are minimal.
You can install video cameras (of course, disguised). At the same time, the number of "initiates" should be minimized so that the thief himself does not know about it, if he is one of the permanent employees - and this happens quite often.
Or set up a trap with the help of money or valuables, as if accidentally left behind, and "special packages" that, when touched, emit a stream of indelible powder paint. But here there is a possibility that not a real thief will be caught, but a “simply” person who could not withstand the temptation (the money is in plain sight, seemingly ownerless, how not to use it!).
You can also conduct your own secret investigation. It is very good if there is a former law enforcement officer in the team: he can, using his previous experience, "figure out" the thief. But again, there is a danger that an innocent person will suffer. Especially when you consider that the thief will try by all means to deflect suspicion from himself.
As you can see, there are no universal and one hundred percent guaranteed methods. Therefore, even if you are absolutely confident in your colleagues, do not leave money and valuables unattended, and when you leave the room, lock it.
As for the pickpocketing thieves, among whom there are the most real virtuosos of their craft, they, alas, can only be caught red-handed, at the “crime scene”. Be attentive and exercise the most elementary vigilance. At the very least, don't keep money and documents in your back pocket! (It is not for nothing that it is called "alien").