Here's where I get a stuck a bit. (this has been mentioned several times) Did he help her or does he just know something? Why would he help her? Give me a scenario where MB could have infuriated BOTH a husband and a wife enough that she would go out and mutilate her and he'd help.
Or if he just knows. Maybe after the fact. And he recognizes her or realizes that she is unaccounted for at 3-5 Monday morning. And he's not going to do anything because if he did, his family would be destroyed. And maybe he'd even get dragged in.
p.s. If this is an average-sized middle-aged woman, then the gun theory becomes more likely IMO (without it, I'm not she'd attack a buff fitness instructor with self-defense training, weighted down in a bulky costume, using tools from the shed.)