To me this murderer is a psychopath. The crime and the plot screams a deadly, brutal end along with fear and control; a control so large and scary the perp is dressed to terrify in combat-level SWAT gear. The notion Missy knew her killer compounds my opinion. That SWAT gear was also designed to protect the murderer as much as it was to disguise the perp and remove DNA (in his/her mind). That perp still does not expect to get caught (though is trembling now, I'd guess) This is deadly planning. It's not a "flipped switch" or a "crime of passion". There are plenty other ways to murder, if that's the case. This may have been planned for months, as I expect. By a few. It took, IMO, one lethal mindset to set the ball in motion and help was a necessity.