I am not exactly on Team BM, and I do know that, statistically speaking, if SM was killed he would likely be implicated. But would LE's actions have been much different if, for example, someone who knows BM (for example, someone who helped with jobs) knew BM was going to be out of town on Mother's Day and perhaps killed SM at the house that weekend, leaving some subtle evidence of a crime but no body and perhaps staging the personal items? Is there anything in the thin file of evidence that we have that would exclude this possibility? The whole scene last weekend when they dug up the cement might be hard to explain, but if they suspected someone involved with the job (besides BM), maybe?
Not that I think this is what likely happened at all, but just trying to think outside the box a little. I greatly respect the tight-lipped investigation that LE is conducting here.
JMO.