And with good reason(IMHO)
It would be amusing if it weren't so tragic, to noting that from the ring wing sources, he was "antifa" because of the "Hammer and Sickle" symbol. To the left wing, he was a Nazi because of the (misidentified) Iron Cross as "Nazi" symbol. And to the Christian wing, he was a Satanist because of the Baphomet Star and a Cthulhu symbol. He was "gay" because of the supposed "Gay Pride Heart. (He also had a Japanese flag pin but I don't think anyone pretends to knows to what this suppose to mean)
He was a "honor Student' but given the state of education today I don't know if he was smart or this just a "pat on the head"
In my opinion the guy was smart enough to assemble enough "symbols' to guarantee to piss of somebody. He was walking Teenage Angst and Rebellion, personified. A real life Rorschach test.
The real question is, why nobody saw this coming. My answer is the school was so large(1,400) he got lost in the system. Mush like other shooters from large high schools.
Every school in America has geeky loner outcasts who wear trench coats with political pins all over them and harbor violent fantasies (don't all outcasts want to "get even" with the popular kids?). Most of them will get through adolescence without ever harming anyone and grow into stable adults. Only after a tiny minuscule number of them snap do we wring our hands over missing the signs. Are schools supposed to enforce "normality" on all of them? "You will not be a dork! You will be normal!"
I don't know.