Unless I missed something (entirely possible) there’s still no good explanation or motive for the Las Vegas mass shooting beyond “I guess he was nuts.” And while there still isn’t a whole lot of pre-massacre verifiable evidence of certifiable nuttery, there is at least one guilt-by-association source of information: his younger brother. If crazy is genetic, there seems a fair chance that these two shared a good dose of it:

Vegas shooter’s brother threatened to kill nursing home employees