The vast majority of atheists in America, particularly those who live in conservative areas report hiding their beliefs from neighbours (often claiming to be agnostic) for fear of discrimination and reprisal.
It would appear that even in the US of A atheists feel legitimately scared of religious people who are decidedly NOT Muslims. 3 Atheist murders in a short period is distressing but hardly above average, it COULD be just a random statistically clump which has no deeper meaning. There is nothing to suggest that this happens more frequently there than among Christians in the USA.
In fact, there isn't even any proof yet that this particular person's murder (or any of them) were even related to their writings - no trials yet, no evidence or motives known. The country is in a state of significant civil upheaval where murders are a frequent ocurrence. That these three victims happen to be atheist may be entirely unrelated to their deaths.
A good atheist should not form opinions before evidence is available and ought to know about statistical clumping fallacies and selective reporting.
Of course it's also possible that these WERE religiously motivated murders - we don't have enough evidence ot judge yet, we don't EVEN have a signficant enough statistical clump to consider it an unlikely coincidence
To get a valid sample you must EXCLUDE the data that originally drew your attention from your data-set, then make a prediction of what would happen if there was a NON-random event, and only if that prediction holds can you rule out randomness. So we now suspect that atheist bloggers may be getting targeted for their writings. We can predict that more deaths will follow, in quick sucession. If another happens -then we can NOT say "4 deaths now" - we say 1 death matching the prediction, if another 3 happen in a reasonable timeframe THEN you've got something MORE than mere coincidence.
Oh - and Muslim extermists are hardly the most violent religious lot around. That title is actually held by a Christian group. The Lords Resistance Army kills about as many people every month as all the Islamic terrorists in the world combined do in a decade - and that was in the decade that include 9/11, in a typical decade it's about a 5th of what the LRA does monthly.
The reason you don't HEAR about the LRA murders is because they don't happen where there is oil or, indeed, any resource of importance to America. They just happen somewhere in Africa, which as far as America is concerned is basically this big country full of children with distended bellies where everybody dies by age 10 anyway.