Interesting, but the reason isn't really shocking is it? Irregardless of the truth, I imagine no company is going to willingly touch that PR disaster. And an overtly racist white guy, is well... I guess to be expected for the most part.
Reading about the guy, grew up Jehovah witness, always had work difficulties, appears to be interpersonal delusions and an ability to relate to people, and sounds like a pathological liar, and, of course, disgruntled employee syndrome with a tinge of supposedly good intentions.
Undoubtedly, a racist move on the guys behalf. Racism doesn't necessarily kill. It only apparently takes a very lonely male with internet access to any given possible extremist ideology, an incredibly broken mind, and a probably not to great life. Stir and sometimes you get... well, young males killing strangers over basic delusions.