Hillary Clinton

Or, perhaps more accurately, my group or my cause or my belief system.

Sounds simplistic, but that's what I see a lot of this justification being. If one is pro-Second Amendment, one can blame it on the Muslims and ISIS and deflect from cultural norms about guns in the US potentially being an underlying issue. Even if the attack is religiously-motivated, that doesn't discount the availability of guns being a factor, etc.

If one is Islamophobic, just blame it on all Muslims (like Trump does) and ignore the possibility that homophobia (religion-based or otherwise) and/or US gun culture could be a factor.

It could be a combination of factors, including all or none of the above. Maybe we should get a little more information before jumping on any particular bandwagon. What a concept! Unfortunately, human nature doesn't always (or often) work like that.

Motives aren't always easy to ascribe. It's the people who think they're 100% positive of the motive immediately after one of these events whose motives are also rather questionable.