Museum experts have used CT scanning to examine the lock's internal mechanism, identify the correct letter combination and solve the mystery.

Neat

"I tried to unlock it for about 20 years, I tried moving the dials, finding the right combinations, and I failed," he said.

I was curious why they didn't just brute force it and try every combination, but this makes sense:

"There are four different rings, and because there are six different letters on each of the rings, there are 1,296 different combinations, and you have to make sure they're aligned with the loop at the top."