Except the results are completely unreliable, so, even as an investigative tool to ferret out bits of information, they are useless. How does one use information garnered from a polygraph when one can't even be sure that information is accurate? It leads LE to chase leads and form opinions based on absolutely unreliable information. That's insanity.
European countries, while not illegal there, do not use them at all for that reason.
Loved your spaghetti/soup analogy
First time I hear that polygraphs are not used in Europe, where I've spend all my life. They are used pretty often, few countries have them admissible in court as expert opinions but even there theyre not not tell-it-all's.
Austria and Germany have them completely inadmissible in court, but they can be used.
Its more like just as a source of possible additional info. If you ask 6 people to do polygraph and 5 of them agree right away while 6th says absolutely not - thats an info. It doesnt mean that person is guilty or hiding anything, they may just feel very nervous and fear of being falsely suspected of lying. So not a proof or clear indication. But then if you learn more about this person and then know that theyre never seemed that precautious before and that refusal stoods out - thats the reason to look at them closely. Not get blind to everything else and zero-in on him cause he didnt wanted to take polygraph.
Or you have a crime almost certainly commited by one person. Few suspects with criminal past. One "passes" with flying colors, rest have it inconclusive or it looks like they were lying. That, depending on the context and additional info investigators have about these people may actually get them interested in that one who flawlessly passed.
Polygraphing & strongly relying on it & zero-in'ing on people who failed is very faulible. High, high risk of wild goose chase and having perp walk free and unbothered.
But thats an occasion to learn more about the suspect. You cant take it as a gospel, but neither you can take witness statement that they saw green truck as 100% accurate. Cause that car could be grey or blue and just appear green cause of the light and surroundings. Or person may remember green truck cause it was the biggest car there. Or you can have someone who just says that to say something and they dont remember anything specific about the car actually.
Have 10 witnesses. All describe different cars, different colors but all say it was a truck and 5 of them remembered distinctive bumper sticker. Thats a good indication to pay particular interest to trucks with distinctive bumper stickers.
Investigations are like this big puzzles where some pieces are missing, some you can be sure of, some you can deem as very likely from this set but you dont know how they fit - but with most you dont even know if theyre puzzle pieces at all.
But back to the topic cause my main point is actually elsewhere as IMO that discussion about polygraphs being useful/not reliable/not is pretty much irrelevant here.
Its not hard to find people who believe that polygraphs are useful - but even with those people, experts, investigators. I remember that from years back, people were just utterly confused. Because...
How do you even polygraph 50 people?
One polygraph done right (still not a tell-all, still not 100% accuracy non-fallible gospel but just
done right - just to even begin looking at it as possibly useful source of info or a point in further conclusions) requires hours of preparation + let's say an hour to do it + some time to analyze it. One expert can reasonably do more than one such test in one workday. Thats easily 2 months of work. To polygraph "just" 50 people.
Take that times four in this case. Cause thats what they claimed to do. Polygraph almost 200 people.
T W O___H U N D R E D S.
~50 people known to visit the party Madison was at. ~150 people were there next day.
One year anniversary of Maddy's disappearance RCMP stated that they polygraphed "almost everyone" from these two groups.
So one expert was doing nothing but polygraphing relentlessly for 10 months straight? Or they have 5 of those and it took them only two months?
Is it probable that it happened this way? That it was preceeded with gathering some info about each kid, gathering some context, taking into consideration that those already polygraphed likely will talk about it with others, that would be just unimagibly immense task. How on Earth they would even get funds for something like this?
That was probably like 10-15 mins thing, with minimal preparation and same or very similar set of questions for everybody:
were you at the party? saw Maddie? heard something? suspect someone? did you hurt Maddy? do you know what happened? & thanks, bye. Or it didnt happened at all and RCMP said that as a way to mislead whoever to get whatever out of it, maybe those who refused to start acting nervously with that sudden realization that everyone else did it but not them.