The only message Stephen Paddock sent was "I am powerful, and your meaningless life is hanging by a thread at any moment, and you are helpless to protect yourself from me or anyone like me." Unless a manifesto pops up belatedly, we'll never know if he had any motivation beyond some kind of personal hate for the irritating happy little world of sheeple, and a desire to publicly execute a bunch of them to demonstrate the ugliness and meaninglessness of life and the futility of delusions of security and control.
Even that's a guess at best. All imputations of motive will be, unless more is learned. Meanwhile, what is behind people's need to make all these big, sinister implications that "there must be some deeper motive?"
They're scared little children, is what's behind it. They're serenely ignorant, and they refuse to believe in the capacity of human evil because it scares them. They believe any act, no matter how horrible, can be "explained" by "ideology."
No. Sorry. Ideology provides the excuse for antisocial violent acts, but the excuse is not the cause. People inclined to violence gravitate towards excuses. One is as good as the other - the one they find will be good enough.
But plenty of them aren't so weak as to need an excuse from some theory or mentor in order to act. To deny that is to misunderstand the problem, waste time and effort on symbolic gestures that neither explain nor improve the situation.
That explanation people want is just some excuse, any excuse, to pretend they understand and to feel better about what humanity is like.
Example: plenty enough people think life is meaningless. Or that people are horrible. Or that humanity is worthless - a bad thing on the face of the planet. That the world is a wrong, bad place and that society is a disgusting lie foisted on people to make them believe in things like the possibility of justice. None of that is insane. It's commonplace.
If you start from nihilism, all it takes is a bit of egotism and irritation with people's chirpiness to want to show them all just how meaningless life is. Which isn't insane, if life really is meaningless. It's just cruel and egotistical. A refusal to honor the illusions of others and leave them to them. A desire to show the world that your interpretation of the world is the correct one, and that they have been fools to believe their rosier views of the world, which protect them not one bit from the inescapable truth.
I suppose you can say that itself would be an ideology, but no. Nihilism is not an ideology. Nihilism is the rejection of ideology.
All you need to kill for no reason is to believe in nothing.