I'm telling you. This is going to end up not being politically motivated. The kid shows all the signs of having a poorly developed worldview with no substantive deeply considered personal philosophy. Most political/ideological operatives will have ample evidence of their beliefs found in SM posts, manifestos, chats with friends, etc. This guy has borrowed gamer memes and silly trolls and not many of them at that.
I think he is attracted to the trappings of political movements because he wants to look cool or he thinks he's being rebellious against his parents (but not really because he probably really loves them, he just doesn't want his peers to know). I don't think he really cares about any of these movements. He probably finds Fuentes, Antifa, Pro-Trans, and whatever else good source material for street cred though he probably doesn't even understand how contradictory that all is.
That being said, it's a big jump to go from mixed-up kid to carrying out an assassination. That is the question mark for me. I suspect mental disorder combined with prescription drugs as the accelerant.
The best way to keep evil men from wielding great power is to not create great power in the first place.