Or have I just missed it somewhere?
It depends on what they mean by "private". I have private files which I keep at the company. They do not go into the public filing and storage. They are mine. Things I did and why it was done that way. Backup in case about 5 years down the road a question is raised.
When I leave the company they will either be destroyed or left with the company. I certainly will not be taking them home with me.
And then there are my personal private files that belong to me and that are not part of company records. Those I will take.
I've thought it if I hadn't posted it; I recall discussing it (offline) with a friend.
I don't know if the question's been posed exactly the way you put it, but I do remember reading comments offered by his widow that he hated typing, wouldn't have typed such a memo, and he didn't have time to put things like that on paper; he kept details in his head.
"How in the world did someone other than Killian's family get his privet records when at least two family members are still alive?"
That's one of the questions which has no answer since the documents were never part of Killian's records. The original reason no one asked of course is that these "ethical journalists" never discuss anonymous sources, or their handiwork.