Because it's a silly question. The airport was bombed in WWII by the US, just like the rest of the country, and Japan wasn't in any war since then, nor was it in any war before then when it would have had such bombs dropped on this location (there was a naval war with Russia in the 1900s, but that didn't result in bombs dropped on Japan).
So basically you're asking for forensic evidence to prove that this bomb wasn't the result of time-travelers or teleporters or something equally fantastical. It's a ridiculous question. Of course it's an unexploded WWII bomb, what the hell else would it be?
So basically you're asking for forensic evidence to prove that this bomb wasn't the result of time-travelers or teleporters or something equally fantastical. It's a ridiculous question. Of course it's an unexploded WWII bomb, what the hell else would it be?