It is an extraordinary claim to say that they "certainly" did nothing wrong. You don't know that, and just as viable of an explanation (even more seemingly logical) is that this is the family of the thief.

However if we accept your notion that they have "nothing" to do with it, the secondary market is what props up the theft market. Many people buy goods from shady actors and with shady pasts ("Oh I've totally lost every supporting component..."), knowing how the sausage is made. Those people should worry about the goods, and hold some culpability in it.