"horrible experience"... blah blah blah...
Somehow your bag got locked. Let me see if I understand what you are saying here. You had a lock on your bag that was secure (i.e. locked), but not locked in the proper location to keep the bag from being opened. Then... just for spite... you accuse a Northwest employee of unlocking the lock, and locking it in place on your bag before the TSA could search the bag. Am I right?
You claimed that "some stupid NW employee at HKG or NRT" locked your bag, and that the TSA at MSP had to break the lock. Possible, but unlikely, as NW emplyees at both locations probably had your bag as part of a rush of hundreds of others. And when you arrived in MSP, you had to claim the bag in order to take it thru customs, right? You did you not notice the bag was locked then? Then you rechecked the bag, where the NW employee quickly handed it off to the TSA screener to be examined.
Personally, I think NW is right. TSA did it. Someone might have thought that you wanted the bag locked, since you left the lock on it. But experiences like yours are why I still use hardsided bags. They might get scuffed, but permanent damage is harder to come by. I hope your venting helped, but all in all, I don't think it rises to the level of a "horrible experience"...
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Proud to be CO free!