Political this, political that. Not even jihad insurgents kill people because religion tells them to, it is just convenient excuse to kill bunch of people. If religion had that kind of power over people to make them kill others then every single religious person would become a murderer in no time. Which obviously was never the case. Soldiers, hitmen, criminals, anyone whose line of work involves potential of killing people do that line of work because they have a hard-on for killing others. Their profession just enables them to do it occasionally without having to face consequences like they would if they killed other people for no reason as civil.
People kill people because they want to. Everything else serves as a way to justify their actions to others. To kill that many people you need to have desire to do it, there is no brainwashing that will make you do it. Even if family lives were at stake, threatened by some shady organization which obviously wasn't the case here or in Breivik case there is no way average Joe could kill 60 in a row. Would stop at some time even if he had ability to start killing.
This dude just wanted to kill bunch of people, everything else media and people like Oberyn make up in their free time, is nothing but pure bullshit.