OMG!! Ae you SERIOUS?????
It's not exactly a deathbed confession, because Kamata apparently died unexpectedly in his own home. But the people who talked to him absolutely didn't think he was kidding around.
I happen to think it's the real deal. But without an ace, world-class autopsy, it'd be impossible now to determine whether Kamata's death was by natural causes or induced, e.g. by prussic acid and other catalogued agents known to induce "death/natural causes".