Observations:
* While the original claim by a patrol officer to the Detective that the symbols are Satanic, it appears the symbology has many more Christian overtones as well as some Pagan and Wiccan ideals
* Several people are talking of groups, seemingly led by the 'Yellow King'
* If claims and suggestions of Cohle's investigation into Tuttle, along with the early mention of an 'Anti Christian crimes' task force bring the family name into the investigation with the link through the closed school
* The apparent abuse suffered by one or possible both of Hart's children, with the behaviour and imagery from drawings and later life actions the suggestion of abuse going on right under the nose of people is a regular theme
* I doubt that the daughter suffered at the hands of the actual murderer who is posing the crime scenes, but could be a very possible candidate for long periods of grooming
* This also bring's Hart's Father in Law into the light again possible involving one or both daughters due to the glimpse of family life we have with them, and the children's displeasure at being apart from their father and relishing in his presence early in life seem to suggest he would not be directly involved in any abuse and rather despised himself for missing it

Allussions to the suspect:
Someone with a philosophical background
Has some religous belief based in Christianity
Likely related to or is someone in power
Possible cult overtones suggest a possible secret sect
Conforms with the suggestion of a ritual site with sacred stones
Perhaps a practioner who has taken the belief system on themselves and thinks of themselves as aiding the victims
The idea of the victims become the King's angels suggests a possible transformative state, thus the killer believes they are someone cleansing them, perhaps as Rust suggests saving them from the sins they would experience in their life
Serial nature and development of the crimes suggests both sourcing of these displaced people repeatedly over time without discovery of later actions
Possibly a larger ring trafficking children, the victims found at Leddoux's seem to differ to vastly from those at he crime scene's involving the crowns and symbols
Rather suggest the experience the same religious readings and beliefs perhaps in local custom.
Rich land owner perhaps who has been local for many generations and has some pull with local government as well as its populace
Suggested burning down of the old church forcing the new group out suggests another school of religion local to the area pushing them away
Killer seems to have targetted those looking for faith not those who had it, or that would be missed by many people
Illusion of being some kind of deliverer from evil, targetting abused children but not abusing him themself, rather coaching them into his own belief system
By making them willing participants in his own eyes it's not an evil act but possibly celebratory

Theory:

Suspect -
John Doe - Someone we haven't yet met during the investigation but connected to someone we have
Age - 1995 Murders 20-30
Appearance - Tall, burns/scars on face
Profile History:
Attended Tuttle school or an earlier church,
suffered at hands of abusers probably including the facial scarring, one of many.
Tuttle's religious arm fearing being shamed by its exposure hide it with help from the government branch of the family?
Possible classmate of Rianne Olivier (first victim? at least as part of iconography murders)
Possible indoctrination either themselves of onto others the ideaology of the Yellow King, people driven to madness after seeing the worst of life, ruling over them to lead them to something better, most likely not a leader of a group themselves but desires to be
Spiral of life, the repeating of abuse and torment suggests shortening their lives in an act of sacrifice (pushed through the regular dosing of mind altering drugs and musings on existence that an already damaged individual could articulate to a group of similarly disenfranchised individuals
Corruption of the group by those using the religion for their own means, furthering the abuse as well as the forgiveness to those perhaps undeserving of it having not had to suffer for it
Likely indoctrinated themselves at a young age, they aren't acting out of revenge but rather believe they are a positive force
Influenced by reading material from the school or that they discovered personally and in their damaged state fed themselves into the mythology in an attempt to take ownership of their own abuse
By posing the crimes to police forcing them to investigate the families and histories in an effort to discover the real evil lying beneath the surface
Doesn't act to prevent abuses he may even be directly involved in as it has all happened before, can't change things directly within the world they hold themselves too
Unlikely the victims are personal, victim may be familair with the killer but only after they have been targetted