A few thoughts about LDT.
I took one once. Failed it miserably. Didn't have anything to do with a crime, and I wasn't accused of anything. Just managed to fail it horrifically.
Then, about 10 years later, I took another one. There was a 'control' question, that I knew I had to lie about (those were the instructions, so they'd get a baseline on what happens *to me* when I lie, and how the machine reads it. The polygrapher was chuckling about three questions ahead...I was already losing control, knowing I'd have to "lie", even though there was no negative consequence for lying. By the time I got to the "lie", he had to adjust the paper several times to keep the needle on it. Afterwards, he told me to go home and congratulate my parents - they'd raised a very honest person who couldn't lie to save herself.
Those two experiences taught me something very, very valuable. There is definitely a valid reason LDTs are not allowed as evidence. One can fail them for so many different reasons, and pass them for the same thing. It's one of those things which, if done correctly, can yield clues to follow up on...but even then, it's not so very reliable.
And my last thought on polygraphing, is that cops can, and often do, tell a person they've failed it, just to rachet up pressure on someone they feel is guilty and close to cracking. The problem is, the person may not have failed it whatsoever; may have passed it. May have passed it with "flying colors". But they're told they failed it. The officers can, and often do, lie to suspects just to gauge reactions and see if they can't pressure them into confessing.
And if TH walked out of one poly because "she was failing", it wasn't her who figured that out. She can't see the graph. That's part of how the area is arranged; the person taking the poly can't see what a "lie" looks like on a graph. So she must've been told she'd failed (and it may have been a lie), and she got frustrated, unhooked and left. But it wasn't her who decided she'd failed; she's been told that by LE who are legally allowed to lie about results and evidence and testimony.
So many people don't realize that LE is legally able to lie about things.
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Herding Cats