Welcome to FT!
Maybe I've missed something, but there is no evidence in your story that the bag was returned to the airport. There are many explanations for other scenarios, including that the person who took it did so by mistake, took the cash and dumped the rest. Maybe this person even went back to the airport and later claimed their own bag. The airport wouldn't necessarily put the two events together. If you saw the CCTV footage, is it really good enough to tell that it was indeed your suitcase?
Why did you put credit cards, money and passwords in a suitcase? These things don't weigh anything and take up no space! Good luck, I hope your suitcase makes it back to you.