I want to believe that Heather's killer(s) have been caught, but is there anybody who thinks it is possible that there is a serial killer (possibly posing as a cop- drivers' licenses on seats of cars) in the area who might also be responsible for Heather's murder? Possibly someone who stalks girls who are out with dates, or girls working at certain places?
Could it be that the drama between the M's and Heather were coincidental to her murder? Could it have been very unlucky timing?
Affairs with married men aren't uncommon, and their wives finding out and contacting the girlfriends is also not uncommon. Someone with no sensitivity and extreme anger might say things that are shocking, but might not necessarily kill the other woman.
I wonder if what was found at the M's house, if not direct evidence of a murder, might be something personal (possibly very personal) of Heather's. Suppose she gave SM a gift of something of hers, and he had it locked away from TM?