I'm watching a documentary about the Rape of Nanking and multiple Japanese soldiers are interviewed, admitting horrible crimes, and yet they aren't being sought by international law. Why?
They were. The Tokyo trials were held during the same time period as the Potsdam trials were held in Germany. Both sets of trials were for the high ranking officials and officers of each country. And both saw about as many people convicted (a rough couple dozen each).
The vast majority of trials for rank and file military were generally held by the countries where the crimes were committed. Something like 6,000 Japanese soldiers have been found guilty for war crimes (mostly right after the war). And something like 900-1000 were executed for them.
I can't speak as much as to why they aren't being sought today.
Three main reasons.
the people you saw on TV may have been too low ranking to matter
the Reverse Course. Basically, the U.S. decided to switch emphasis in occupied Japan towards fighting communism. So to this end they stopped working towards punishment of as-yet unpunished people.
when the U.S. occupation of Japan ended in 1952, they turned over the prisons and administration of imprisoned war criminals to the Japanese government... And the Japanese government freed them all. There was (and is) a widespread feeling in Japan that the war crimes trials were unfair because it was ex post facto justice--it was the punishment for breaking laws that didn't exist at the time the crimes were committed. So the war criminals who had been executed were out of luck, but all the imprisoned ones were now free. The Germans didn't do this, though, so war criminals stayed imprisoned longer there.
They are and were. There were trials held in Tokyo regarding the war crimes committed by the Japanese soldiers in World War II.
The difference is, most of these war crimes were committed by soldiers. So it was hard to find everyone responsible. Unlike in Nazi Germany, where all the perpatrators were either high nazi officals, or special forces such as the SS or the Eistanzgruppden
A little off topic, I have read that many high ranking Japanese that were responsible for the warcrimes could be charged but were not as the allies feared that charging them will cause unrest among the Japanese population.
Scientist from unit 731 who did many lethal human experiments were not charged as Douglas McArthour gave them immunity in exchange for their research findings.