I prefer it when they give a reason first (like in a note), and then kill themselves during the process. That way, not only do we avoid having to do 20-some years of death row, but we also know the motive. Fortunately, that did happen here, so we know that it had something to do with a thing that happened to him 20 years ago. In other words, he was a nutcase with a grudge.
There is no "motive" that justifies evil. We learned that on 9/11/01, if not before.