More in depth article from Reich: https://www.nytimes.com/2018/03/23/opinion/sunday/genetics-r....
Perhaps there is no hard evidence because nobody is willing to risk their lively-hood over researching such claims. Just look at what they did to Dr. Watson. Heck, a few paragraphs above Reich was talking about African-Americans being genetically predisposed to prostate cancer as if it was a highly controversial topic.
Regarding school shootings in particular, my personal guess is that such sour actions on the average are merely a symptom of a hole in America's conscious, in that these semi-affluent white boys have lost meaning in life, and do not care if the actions they commit are grave. Of particular note is you do not see boys of abject poverty commit these actions, as they are more focused on not starving (and thus have something obviously meaningful to their life to prioritize).
Well that's certainly better than the third one.