One angle on the difference in reactions to NZ are
1 - perpetrator was one of us
2 - location was our friendliest ally and country most similar to us on virtually every score
3 - NZ largely terror free until then (place least likely to be a target?)
There have been some massive Muslim v Muslim bombings in / close to mosques with similiar death tolls. They attract minimal news coverage and little comment. (Reflects our western news bias....eg train derails in Pennsylvania, three die, makes evening news here. There would a train accident every week that big in India..zero coverage here... the biggest example of this bias was the Boston marathon bombing hysteria ...yanks are sort of like us, we have marathons...)