Also maybe subconsciously this was a way to force themselves to commit suicide. Like, they hated their lives, so they decided to do something so terrible that not only could they live with themselves, but they would never have any hope of a good life again. They probably could have gotten away with it, but they made it so obvious that they did it (and when it wasn't particularly obvious in the first one, they made it so with the second). Then they could have turned themselves in, but instead they went so deep into the wilderness that they probably would have had no idea how to get out even if they changed their minds. They put themselves in a situation where suicide was the only good option, and I think that was one reason why. I don't know how much of this was even on a conscious level. Just speculation.
You just explained what is basically the very core of "extensive suicide" . The person contemplates suicide but is unable to plan a way to do it, all by themselves. They decide they will do it after they have killed others. The killing of others can be more appealing and exciting (thereby giving the subject the motivation to carry out the suicide or resulting in being boxed into a corner and killed by police).
They can even gameify it. In fact, we could say that the legends of Butch and Sundance or Bonnie and Clyde or any number of solo serial killers) show how it can work (until it doesn't, and the players are dead; game over).
The article on gaming and psychopathy (linked upthread, but I can find it in my bookmarks) talked about how two different players find themselves in a new game world, with almost nothing.
One player previously has learned to make friends with others in game, in order to further his own goals. The other player thinks it's funny to kill strangers and take whatever stuff they might have.
The first player was shocked, beginning the game with his new teammate, that the other person immediately destroyed the first stranger they met (and laughed about it). First player was irritated, too, because that new person was basically unarmed, but might have been interesting and useful to have along (remember, all these characters are operated by real people out in the real world - not by the computer).
During World War 1, both sides used soccer to gameify aspects of war in the trenches, particularly the British (for whom it was rather successful).
Underlying all that, though, had to be the very real knowledge that they were on their own suicide mission (MOO). That had to become conscious at some point.
As suicide rates in their age group rise in North America (and elsewhere), we can expect more of the extensive type of suicide, in which the suiciding person decides to take others with them.
