We may need a different thread, that discusses and analyzes each of these cases. I have been actually correlating similarities between these events since Ted Kazinsky, Oklahoma bombing, Columbine, all men who have become marginalized by society. Bullied, and unable to achieve in a world that they don't fit into.
They had a rage against society, and they reacted with violence, because of their absolute perceived helplessness. The plan to kill empowered them, and gave them an identity, something that they could actually accomplish. The planning gave them a feeling of power, that they could control something in a world that they have zero control over anything.
Imagine, if you can't hold down a job, because you don't "fit" in, for whatever reason, you can't make friends, no one wants to talk to you...people avoid you. But, you can fantasize about what you can do to have that control over those people.
This isn't about race, politics, religion, it is about society now, and how our post industrial age relies on people being able to work with other people. If you don't fit into the cookie cutter mold, you are discarded. These men reacted with violence. And I have no doubt that there will be more shootings, bombings, knife attacks...