self serving. A lifetime habit. What he wants, and was probably flattered by the journalists request, is a bit of a back rub, a bit of feminine understanding, a bit of masculine propping up. All his life , he's said what was necessary to get him what he wants, why change habits midstream?
And it got him what he wants. His main audience is his fellow convicts, and his main aim at this point is to lay down the foundations of a man of consequence while serving a life sentence. Nothing more. No other motivation. A man of consequence gets an apprentice journalist to publish his apologia, his plea for understanding, his explanation, if you will of what he did. He really believes that is what the letter does.
It's a dog eat dog world in Supermax, and he has to hold some aces going in because he wont get any once he is in there. He is up against the likes of the Murphy Bros, Ivan, Ivan's nephew, de Gruchy, Sef Gonzales, who has whinging down to a fine art, all sorts of old hands..
good luck, Holdom You'll need it.