In keeping with your theory, I myself have wondered if the intent of the intruder was to commit a break in in order to show how easily the church's current security could be exploited, as a push to get a more $ophi$ticated $y$tem. For how long that disguised individual was inside the building, well, hardly anything was vandalized. Remarkable really. It's like a slo mo movie of someone trying really hard not to do any real damage.
If not for MB presence and subsequent murder, when would the intruder have left? Daybreak? Wait until first staff arrived?
Or was someone going to review footage and be startled to see how effortlessly they'd been burgled, conveniently recommending a higher priced plan? Who would gain from that?
Could it be that a person like that was specifically targeting a rainy night, as insurance to anyone else being there?
Possibly caught by surprise when MB entered? Panicked, reacted, over-reacted, blungeoned/punctured/attacked, for fear of being found out?
In any other context, never a murderer. Not before, not after. Plagued with guilt but in no hurry to have either part of that exposed.
Maybe?
JMO
