So, they checked all RSOs in the area and do not think the perp is in that group.
Maybe a RSO outside of that area, that came to the area?
I still think it was sexually motivated and RSOs are not RSOs until they are caught and register.
There are a lot of SOs out there that have not been caught.
If I am wrong and this was not a sexually motivated crime, I then think maybe a minor or group of minors. There have been several cases recently that show minors can be very "dark". IMO that is due to cultural changes that have to do with tv, music, video games...that act as tho human life is disposable. But, that's a whole different topic.
But my 1st suspect would be a sex offender.