If you're trying to understand Micah Johnson's motivation for his attack on Dallas law enforcement, you might want to compare his case to that of Mark Essex. I don't know, maybe it will help.
I first became aware of Essex's shooting spree when I read chapter 8 of Elliott Leyton's Hunting Humans: The Rise of the Modern Multiple Murderer. I was just re-reading Leyton's analysis, and I realized that one of his main sources, which I had thought was out of print, is actually currently available in paperback. I'm referring to Peter Hernon's A Terrible Thunder: The Story of the New Orleans Sniper.
Obviously, I haven't yet read Heron's book, but it's now on my reading list.