I expect that there are techniques used by LE to encourage witness participation.
AM said that he was reluctant to consider BM as a suspect because he told him that he passed a lie detector. LE corrected that misconception. They also told him that BM's truck data did not match his story. As a result, AM was clued in and recognized items of his knowledge as troublesome. He could see things in a different light. He
became the advocate for Suzanne that was lacking.
I'm guessing that LE will often share information, without which, the witness would dismiss what they knew, as irrelevant. I haven't got a problem with that.
Moo
I believe that AM has come by some of his info courtesy of LE, but I'm sure he's heard plenty from other reliable sources close to SM as well, e.g., close friends, other relatives, etc.
Not for one second do I believe that LE has shared a single thing with AM that would jeopardize their investigation.
If BM refused a polygraph, then he obviously already knows that himself.
Likewise, if BM provided a version of his movements that doesn't align with the movements of his vehicle, then LE has no doubt already pressed him on that point.
In fact, we know BM already knew his timeline was *advertiser censored*-a-doodle-doodoo, because he brought it up in one of his interviews with Lauren.
Basically, I think LE made a decision to share with SM's family only as much as they needed to know in order to sense which way the evidentiary wind was blowing.
It sounds like they managed to convey to her family that BM was being less than cooperative without disclosing to family members any specific evidence they've gathered.
Some of her family may have been harboring a false sense of loyalty to BM because of the fact that he's SM's spouse, and he was feeding them a bunch of malarkey about how he was being completely cooperative and doing everything LE asked of him, "I've answered every question," claiming he'd taken a poly, blah, blah, blah...
I respect the move by LE to set the record straight with SM's family, because it gave them the heads-up that BM was not telling them the truth.
Her family might have been reluctant to share info about the marital relationship with LE, given his portrayal of himself as a distraught husband doing everything he possibly could to find SM.
Once LE disabused SM's family of that notion, I'm sure they realized that sharing inside info with LE would be anything but an act of disloyalty.
On the contrary, full disclosure of any and all known facts, no matter how personal, would be the ultimate act of loyalty.
Loyalty to Suzanne.
JMO.