My sympathies to the families of those involved, death is always a tragedy.
As for the people worrying about the possability of a backlash against video games for this, of course there will be.
As for if I think video games are the cause? No, I'm not just saying this because I am an avid gamer (although I guess that does have a bit to do with it) but because I think that most people are complex enough that it would probably take more than one easy to identify and rationalise thing to drive someone to an irrational act of desperation like killing a girl for her earrings.
There are probably people out there who do let their love of games go too far and do horrible things as a result (the same could be said for many things though, how many murders have been committed as a result of the Bible and other pieces of literature?) but to say that the medium as a whole has a corrupting influence seems to be avoiding the real issue in favour of something easier to blame and rally against.
I personally believe that the cases of 'video game addiction' probably stem from deeper issues, I'll admit I used to be very bad about my gaming habits during my teens (during which I had pressures from school, my parents fighting and breaking up, obvious changes going on at the time, my own inherant social difficulties and other issues), I didn't feel like I could talk to anyone or do anything about it and playing games was at least something I was really good at and helped me forget the stuff that was troubling me (rather than having my problems weigh upon me I could simply turn around and reduce them to a fine paste with a chaingun).