While all sources claim to still not know what caused Mr. Paddock to behave in such a manner we sometimes forget the obvious link and look for any exotic possibility for relief. From ISIS to gambling and everything in between has been suggested.
How about this one: It was reported that Mr. Paddock was using a prescribed anti-depressant drug. Therefore, the killer's motive may have been beyond his control.
Perhaps the motive is as simple as this: "possible side effects."
How many past recorded violent episodes, murder/suicides, were the result of side effects from "feel good" drugs. These drugs can create a numbing effect of most human values as well as distort their true reality, with suicidal tendencies. (Robin Williams comes to mind. Did he ever scream in bed too?)
If the pharmaceutical companies don't silence the possibility of such a cause then Congress should delved into the many new prescription drugs that do spread killings as a sidelight.
....Prescription Drugs Do Kill And Can Also Create Killers!