I am reminded that we never found out the motive of the murderer who massacred 58 people in Las Vegas in 2017. Six years afterward, there was a suggestion that he might have been angry at the casino, but they still don't know for sure and will never know. Only in fiction do murderers always have a clear idea of who they want dead and why. When I think about local murders, the "motive" is usually that someone was drunk, high, or psychotic, and angry at a friend or relative.