Update: June 11
The New York Times published a PDF of Holmes's handwritten composition notebook, 36 pages, here, rather like a crude manifesto (a small version of Unabomber's). There is concern about no sense of justice and about the "strong, average and weak". But the answer to "why" there is free will (p. 33) is simple to answer. It's to counter entropy. Good decisions by people (or any beings with free will) decrease entropy. Enough bad decisions, the universe could fail. (With the Cuban Missile Crisis, the world almost failed in 1962, a bad time in my own life.) That sounds like the metaphysics of it. So choices really do matter, in the sense of quantum physics and cosmology. They call it the law of Karma.