Simon, I am pretty sure we all understand [even if we can't begin to imagine] how much devastation the murder of a loved one can be, and doubly so when it goes unsolved, the not knowing who or why must be excruciating and make it very difficult to move on.
However, the 'light' response is twofold - firstly, there is a possibility the thread was started simply in the hope of a general police directed rant, which in light of our current clampdown on threads that get all too heated and over-excited, the response is probably the best way to stop it going that way.
Secondly, as ghoti said much earlier, murder cases always remain open and should any new evidence come forward, the investigations will be resumed. However, the chances of new evidence in some of the earlier cases in that list are at best, several million to one. Can you blame people for being amused that the OP has posted such an extensive list with which to try and make his point? It is also human nature to joke about such realities, because it is a coping mechanism that has got us through many, many horrific events.
However, I am sure the family you know are devastated and I am also pretty sure that as a forum we all wish that they can find peace and the culprit sooner rather then later.