It has always surprised me what people are capable of and how even blood relatives will give in to the temptation to steal. My father as an accountant caught many thieves within a company, more often than not it was someone's son, brother, or otherwise. I have witnessed entire blocks of stamps disappear when inventory wasn't controlled or a plumber that was doing side business with the boss's materials. It is unfortunate when it happens, but if you have no controls in place and no method of tracking how long will it go on before you find out? There are many methods of tracking that can improve awareness and reduce shrinkage. You can take any actions you choose once you know, but staying in the dark is rarely the best option.