Since the evidence hasn't been revealed yet (we're putting our faith in LE), we don't know the totality of the evidence.
I know the chances seem slim and everyone here believes the Moorers are responsible for Heather's disappearance but what if only one of them really knows what happened (where Heather is)?
What if, for some reason, neither of them know where Heather is?
Until we hear all the evidence, how can we be sure?
If only one of them knows where Heather is though, then they'd be unable to turn on each other for the purpose of revealing her location. But they could turn on one another to say he or she committed murder. Still, the one who knows, wouldn't tell where they put Heather. But we're assuming they both know, right?
I'm not sure what everyone else is assuming. I think this way:
If both killed and know where Heather is, neither will say anything. There isn't an upside unless they are handed some really sweet deal, and I can't think of one that would be acceptable.
If neither killed Heather, but know where she is, they would have said so by now. (If she had run away from life)
If neither killed Heather, or know where she is, all they can do is find some way to refute the reported evidence that LE has. And both will say nothing.
If one killed Heather, and both know where she is, the one that didn't kill her is still an accessory after the fact. Once again, there is no up side to saying anything unless they get some kind of sweet deal. We aren't up to the sweet deal point, yet. That might come Monday.
If one killed Heather and the other has no idea what is going on, either A) They are pretty darned stupid or the one who killed her is incredibly brilliant or B)They would have had to have been in two completely different places during the time what happened to Heather happened AND NOT NOTICED OR CARED WHERE EACH OTHER WAS. Say SM was home with <Mod Snip> and TM was out killing Heather. How would SM not know TM wasn't home? And how would he not wonder where she was at, especially if Heather went missing that night. Same reversed. Unless <Mod Snip>, and TM and SM were just out wandering aimlessly separately, I just cannot see one having no idea what happened if the other is guilty in this particular case. So calling this thought "One killed Heather and knows where she is and the other didn't kill her and doesn't know where she is", the one that doesn't know could only bargain with any information they would be willing to give about the other one being missing, and anything suspicious from that timeframe. And since they didn't come forward in the beginning, a sweet deal may not be on the table.
I forgot, If both killed Heather, and they have no idea where she is at (put in the river, left somewhere but the body is no longer there, what have you), they have nothing to bargain with except telling on the other. If both are equally guilty, any deal they get will not be very sweet at all, so no real advantage to saying anything.
Yes, I really do run all those things through my head (plus some), which is why I am fence sitter extraordinaire....