[adonig]

"It apparently didn't occur to them that if I were a real Japanese spy, I might have brought the glasses with me from headquarters."

I'm not a criminologist but I think they might have classified the glasses and the glasses case and maybe found enough evidence indicating that the glasses have been made in the U.S. or maybe even in San Diego.

Even if they didn't, then it's still their job to do exactly what they did and they were successful. They found the real owner of the glasses and were able to confirm, that the person isn't a potentially dangerous enemy spy. That case can be closed and they can do something else.

[adrianmonk]

Also, it's plausible that a Japanese spy would buy new glasses in the US. It would probably be smart. Why take a chance that someone will notice your slightly unusual-looking glasses? Just get new ones that look normal.