Originally Posted by
Dave Noble
Based on the requirement for liability on unchecked baggage as per article 17 to be BA's fault, I would think it would be a hard case to argue that another passenger taking it was BA's fault
You omit the part where the op mentions that the bag was moved by BA staff though I'm unclear why it was. Whilst not a sure solution, I'd argue it means that inadvertently, the airline arguably took some responsibility it wouldn't have had otherwise.