One thing I wonder though; how common are these type of crimes in other 1st world countries?

I’ve heard of such things happening in other countries, Europe, Australia, the UK, etc. Crimes like these even happened in the Communist bloc pre-1989, though they were pretty well hushed up…

http://en.wikipedia.org/wiki/Olga_Hepnarov%C3%A1

The Hepnarova case actually seems pretty similar to this one, though of course no guns were involved, and the perpetrator was a woman.