This is just my opinion, I am not a professional. I've been reading about this stuff for years (both SK, Regular Killers, Sexually motivated crimes). This is a blend of those because we really don't know, but just my opinion. Maybe it will help narrow something down or help brainstorm other avenues. Some things are taken from research, put into my own words.
Person is most likely shy, but anxious, appears reserved and experiences feelings of inferiority; taking refuge in fantasy where they become omnipotent and powerful. The more they enter into the imagination, the more real it becomes until the crime(s) is committed. This imaginary world gets so familiar, it’s inevitably enacted. With victims older than 5-6 as in this case the person is most likely outside family, but not unknown to family, in fact they may know of them. The age is probably a 19-42 yr old and male. They are most likely familiar with assailant and are most likely a victim of abuse and could easily be described as mentally Ill by friends and family. Prior legal troubles, both financial and criminal, with few but often acknowledged bouts of losing control witnessed by others. The unsub most likely killed for sexual gratification and/or possibly in fear of being caught if they knew more about the family or victim and felt the family knew them too much. Research says the suspect is not family, was sexually driven, and probably killed with weapons.This person would normally be at the site for legitimate reasons either living close by or visits to the area often through routine (work or recreation) and probably made initial contact before the crime within a ¼ mile of the crime scene.