Whoa! Let's not get carried away. The notion that it's a serial has to be bolstered by many things. The single most important thing that sticks out in my mind for that is - there has to be more than one.
Let's look at it for what it is and what we know.
It is a terrible and by all accounts brutal murder of a young girl. It is an extraordinarily sad thing that happened to (by all accounts since I don't know them personally, though I have no reason to doubt they're any different than myself and my family) a good family in a nice neighborhood. She was a minor and that is undoubtedly the reason there has been no further word on anything from the police. It smacks of a rage killing moreso than anything else, and rage killings are directed at someone and there is a reason for them happening. It doesn't appear random at all, the neighborhood is relatively quiet, there's not many police running here (at least not more than you would expect when something like this occurs). There are sex offenders in the neighborhood, but I don't know of many areas that have a population over 75,000 people that don't have at least one. We have more since the jail is nearby as well. The sex offenders in this area have been convicted of non violent crimes, heinous as a sex offense is, I didn't read one that was of a violent nature (and I've read them all, I make a point to every 6 months or so because I do have a young'un).
Serial murders, while grisly, have certain elements to them. I haven't even heard in rumor anything that would suggest that to me. Going by the definition of serial murder, as Robert Ressler defined it (he's the originator of the term based on very specific criteria) the manson murders were spree murders not serial killings. Incidentally he is a terribly fascinating man, and I highly recommend all of his books.
http://www.robertressler.com/
http://en.wikipedia.org/wiki/Robert_Ressler
). I was sitting here and asked myself, what's a good name, I took another bite and "mmmmmmbrownies" was born. 
