Police have repeatedly said RL is not a suspect.
Based on that, perhaps we could focus on and discuss:
Motive
Statistics of it being a SK
Similarities to other SK or crimes
As LE stated, "Why Delphi?"
Would anyone else besides me like to sleuth the crime?
I keep trying, but don't get much response. I'll try answering your sample questions as well as I can.
Unfortunately, I'm guessing the motive is the usual one in the abduction/murder of young girls. I've seen nothing to indicate that either girl was into anything illegal; they don't seem like the type who push people to the point of violence (they strike me more as people pleasers, but I could be wrong about that); I feel like someone involved with a gang would do something to make that at least somewhat obvious.
I have no link to a source, but I've heard that less than 1% of murders are committed by serial killers. I think the odds of one being responsible for these two may be higher than average because that number includes all murders - most done by someone the victim knows but not family or intimate relationships, many are done by family, boyfriend/girlfriend, exes, etc., many are gang related, and so many other types that don't fit here. I do believe that if the person isn't convicted of this crime, he will try again eventually. In my mind, if he isn't a serial killer, he probably will become one if given the chance.
Obviously, the deaths of Lizzy and Lyric seem similar (although we really have no idea if they are since we don't know the circumstances of either pair of actual murders). I thought Amber Hagerman seemed similar too, but all of the other girls are younger. I've found some others that seemed like possibilities, but don't have any other names handy right now.
Why Delphi? I think it was convenient at the time. It's a rather peaceful area, so people are/were more trusting and easier to deal with. It's a smaller town, so it wouldn't immediately have the same resources available to big cities (that may have turned out to be wrong, they got help in pretty quickly.)
I may not have any of the answers, but at least I have a few things for people to disagree with! All MOO