[marktwain]

I once read that Japanese consider a murder-suicide within a family to be two suicides.

Yes, this is true, although it could well be more than two. It is called a "family suicide". However, it doesn't affect the rates very much, because the total number of "family suicides" is relatively low compared to the total number of suicides.

[DTogo]

Muri shinju

Usually involves a woman and one (or more) of her children.