Those are different. If someone is assaulted in his own house and he knew the assault was impending, and did not try to stop it, then I would say it is his own fault, even though obviously he did not kill himself.
If the babysitter was in danger and the owners knew about the danger, yet still let her babysit, then yes, it is the owner's fault the babysitter is injured now. Obviously the assailant in both causes caused the damage, but the fault of letting it happen still goes with the owner in either case.
It is the same with the Wal-mart situation. The owners knew a mob was gathering and let it. Instead of either hiring enough raw power for that day (in the form of security. And another brief tangent, don't even try to say Wal-Mart had no intention of having a mob, thus did not hire security. All major retailers know insanity of black friday, and it is Wal-Mart's fault for not adequately planning for it) or closing their store, or telling their employees to flee the scene, they did nothing. And because of that, a man is dead now, and a few people injured. To stop it would have been all too easy for Wal-Mart, but they did not, and they must accept the consequences.