He knew perfectly well (even if he wasn’t inclined to admit it) that the material body had a spiritual aspect. He knew that “spirit,” however explained, was real, because of his own undeniable experiences - which, though he might suppress them, he couldn’t altogether erase from memory.
We’re constantly changing facts, rewriting history to make things easier, to make them fit in with our preferred version of events. We do it automatically. We invent memories. Without thinking. If we tell ourselves something happened often enough we start to believe it, and then we can actually remember it.
If a memory wasn't a thing but a memory of a memory of a memory, mirrors set in parallel, then what the brain told you now about what it claimed had happened then would be coloured by what had happened in between. It was like a country remembering its history: the past was never just the past, it was what made the present able to live with itself.
The ones who did it can always rationalize their actions and even forget what they did. They can turn away from things they don't want to see. But the surviving victims can never forget. They can’t turn away. Their memories are passed on from parent to child. That’s what the world is, after all: an endless battle of contrasting memories.