tomkat, there are multiple motives for decapitation of victims. Although hiding evidence may be one of these motivations, I am leaning towards the motivation being sexual in nature by a ritual killer/s.. Imo, the decapitation may be for confusion/deflection purposes;
to hide the evidence, and identity(dna) of a sexual assault by a sadistic escalated ritual predator/s..
Is there an evolution or elaboration to the ritual murderer?
http://www.jaapl.org/content/38/2/239.long
Ritual and Signature in Serial Sexual Homicide
www.jaapl.org/content/38/2/239.long
by LB Schlesinger - ‎2010 - ‎Cited by 10 - ‎Related articles
Address correspondence to: Louis B. Schlesinger, PhD, John Jay College of ... Authors of other early publications25 found similar behavior in sexual murderers. ..... victims and
progressed to decapitation and then evisceration of later victims.