As has been pretty much the case with every nutjob mass murderer. About the only one that hasn't been shown to have been throwing red flags for years is the Las Vegas murderer and so much of the info from that has been either suppressed or mucked up it's hard to say
It could be simply that he was a semi-loner who never had any law enforcement record, and that at 64 years old, he was on the very tail end of the phase 1 baby boomer generation, and as such, he just didn't have the onlie/social media trail the modern news cycle is used to digging into and fleshing out the story with.
His father was a notorious criminal, and his brother who went on TV was... weird as hell. In a way that either screams mental illness and/or personality disorder, or he's going on some kind of rapid-fire sociopath scam-artist speil.
Could be simple as that. Bad crime genes, and above-average logistics and planning that went into his attack. The rest of the "secrecy" could just be the LV city, county, and state authorities treading softly because of the #1 nature of casinos as economic drivers, tourism, employment, and tax base etc.
What is more interesting is the larger picture of how familes, social institutions and/or government handles the potential mass shooter. And the media role in perpetuating mass shootings.
Some aspects of the “mass shooter problem” are somewhat intractable. The “guns” issue is moot, because we won’t give them up, and the 2nd Amendment prohibits it. And if for the sake of logical argument, one creates a given that complete confiscation was acceptable, it’s logistically impossible anyway. And that even if we lower the bar even further to say confiscation was acceptable and possible, alternate methods of carnage like arson, chemicals, IED’s, large motor vehicles, structural failure, or creating human stampedes/crushes etc. could well be actually worse in the long run.
The media side of perpetuating the viral meme of a mass-shootings as a way for the disaffected to lash out is possibly also impossible to fix. 1st Amendment grounds make it impossible legally. And if we again say it was for the sake of argument, we’re disregarding all the other negative consequences. And voluntary methods by the media may not work either. Such as the idea of never identifying the shooter, and changing the obsessive nature of the way incidents like this are covered. The one media outlet that decides to buck the trend and report it anyway could well be rewarded with ratings and viewers. That would make that sort of gentleman’s agreement worthless almost instantly. That’s certainly proven true with almost all other kinds of sensationalist and tabloid content. The only thing that could ever really suppress the viral meme nature of mass-shootings would be a sea-change in the entire American populace, voting with their viewership. And I have no idea how that could be accomplished.
That leaves us with what can be controlled… maybe. In theory we already have multiple routes by which a troubled person can be identified and get intervention, medically, legally, or both. And here, we seem to have two extremes, and a really big unknown in the middle. On one end of the spectrum, we have the now familiar string of missed opportunities on the part of parents, schools, social services, doctors, law enforcement and courts. Either because they’re reluctant to stigmatize someone, or “ruin their life”, or because of more nefarious reasons like trying to suppress crime statistics. On the other end of the spectrum, we have the cases where someone gets intervention, and has “their life ruined” when it wasn’t warranted. The cases where a kid chews toast into a toy gun, or draws a combat scene of some sort, and is suspended/expelled. Or a vindictive protection order is granted in a divorce. Or some person with no ill intent gets wrung through the police and the media because they live in a more anti-gun area and owns firearms.
In between those two extremes, we’ve got the cases where maybe the intervention was warranted, and maybe a mass-shooting event was prevented. And of course, it’s impossible to get any kind of count on something that didn’t happen. Perhaps some kind of objective criteria could be generated from both the “successes” and from the “failures”. What would that objective criteria be? How could it be applied in a fair and consistent manner? Can that be done in a way that does not violate the civil rights of someone who has not committed a crime?