"That's a long way of saying you can't back up your claim"
YOU PROVE THAT THEY ARE NOT!!! (capitalized for emphasis not yelling).
All liberal sources are extremely unreliable. The left has absolutely no problem just fabricating stuff. I see it happen all of the time. There is NOTHING you can show me from any leftwing "news" source that I would ever trust.
That being said, all the time I was looking into finding out if there was any clue about a mass shooter's politics, I basically search the regular mainstream leftist news. When I found it it was later article, either later that day, the next day or later. The reporter was trying to write a background piece on the shooter. Sometimes they would just come right out and say it, other times I would find clues because they didn't want to come right out and say it. It would be either a comment the shooter made to someone or the people he hung out with or whatever.
What pissed me off is when ABC reported on the theater shooter in Colorado several years ago, they got the guys name and found someone else in town with the same name who had been a Tea Party member. It took them a while to realize that they were putting the blame on the wrong guy and the actually shooter was a leftist. A leftist who intentionally went to this theater because they had a no gun policy and the one by his house didn't.
I think I have told you before, that these guys are psychologically disturbed FIRST and political second, third or whatever. It is possible that being a left wing nut job is completely irrelevant for the justification they made to go shoot up a place. However, there are plenty who go shoot up a place specifically for political reasons.
And the fact of the matter is they are not conservatives. Most conservatives are Christians and Christians are commanded by God to love their neighbor as themselves. Most Democrats are atheists and atheists have no morals, other than the ones they borrow from the Christians. There is no standard by which they live their lives other than whatever the Democrat Party tells them to believe. And if you have nothing to live for then you have no reason for existing or letting anyone else exist. And that is why most mass shooters are leftists.