Update

Reading and watching interviews with the man's grief-stricken parents.

• The man was clearly mentally ill and was angry at the police for taking his son from him.
• He was white.  
• His father is moderately right-wing, blaming "liberal people" for allowing his son to be taken from him and saying that there is no help available for white males.
• His mother says he was obsessed with the news, but not in any ideological way.  Every time a bad thing happened, he would say that he had a precognitive warning of it and tried to warn people but no one listened.  She was also emphatic that he did not have any advance knowledge of any of these bad things.  And she had no doubt that he was mentally ill.
• It was, in fact, his mother who took custody of his son, presumably because of his mental illness.  She feared that he would violently retaliate against her.
• There is some suggestion that his parents are divorced.  They have different last names, and apparently the father was not involved in the custody dispute.  (Interestingly enough, at least in the part we saw, he neither defends nor criticizes her actions).
• Naturally, both parents are devastated.

So, all in all, this looks like a personal feud without political motive.  At least so far, there is nothing to link the shooter to any political movement whatever.