He should be on this list: https://travel.state.gov/content/travel/en/international-tra... But there’s nothing.
https://jp.usembassy.gov/services/death-of-a-u-s-citizen/ Nobody was ever able to get any of the documentation listed on this page from the Japanese side, even family, and the Japanese continually report they have no record of the death. There are also no “blotter” style documents in Japan or the USA documenting his death.
I’m willing to be proven wrong - and accept others will not believe what is hearsay to them - but as someone who has been involved in emulation for years my Bayesian prior is extremely, strongly on the side of him being alive.