If that's true, he would've talked a long time ago. He refused to talk to many investigators from various states who also could've gotten the same letter not seeking the death penalty (presuming the guy was already convicted for life), only Holland got him to talk. So, yes Holland is partly if not entirely responsible for getting him to talk.
I read the article, Holland definitely got the guy to talk through unconventional means. He has killers draw their victims. He seems unaffected by the flat way the killer describes his victims. It’s almost like becoming the killers “advocate” (lack of a better word) instead of prosecutor.
I’m not claiming you’re wrong; I’m just curious—are his methods actually unconventional? Once a person is serving a life sentence (nothing to lose), and there’s nothing his cooperation can do to get him out of prison (nothing to gain), it seems pretty obvious to me that anyone wanting to work with him would need to try something like what Holland has done.