However, the dirtiest thing is to use all kind useless evidence and intimidation techniques to scare otherwise innocent people into taking plea deals. This whole guilty plea saga is a disgrace to the justice system.
Recordings of interrogations that feature them also show that they tend to come along with other appeals to ethos ("this is doctor so-and-so...") and hand-wavey forms of intimidation like touting their "seriousness" or "efficacy".
Anything that requires a person to "interpret" its output is likely not very deterministic, and so likely not very reliable for establishing... anything. This is akin to palm reading or graphology.
Unfortunately, revealing to the police in such a situation exactly how foolish they look by getting behind such a device isn't exactly advisable either!
That's not the only place where they can be used, and cause damage.
Video evidence of me entering the store, using the atm, and immediately leaving the store? That was not evidence to them because I failed the polygraph.
I take an exceedingly dim view of any police department that uses a polygraph in any capacity. They've been proven time and time and time again to be worthless as a tool, but police still use them. The rough equivalent is using tarot cards as a tool for solving crimes.
Eye Witness Testimony for example, aside from the fact the people are terrible at recall anyway and High Stress causes memory problems above and beyond the normal memory issues of the human mind, it is very very very easy to manipulate a victim either directly or indirectly to identify the "target" no necessarily the actual criminal
police "drug" dogs are another one, it is more or less a blank check to probable cause for a search.
Then there is one people never even question because it is the foundation of the legal system, the good old finger print... It always amazes me that with DNA it is always probabilistic, "1 in 4 billion people will have this same DNA" but with Finger Prints is an absolute, Match no match.. Call me crazy but I don't think that position is scientifically valid
They don't even need to do that. They can just lie to you. "Hey, your buddy just totally ratted you out in the other room, you better tell us your side of it if you don't want to take the rap for everything"
They can tell you to just say you were there, and they'll go easy on you. You lie and say you were there, now they have evidence that can actually lock you up, even if you are a random person off the street.
For example, in this case police threatened to arrest the mans wife if he didn’t confess to killing his child (a new trial was ordered): https://brooklyneagle.com/articles/2014/02/20/police-can-lie...
But they went on to say it was still acceptable to lie to suspects... I imagine this murky area of the law will eventually say that police cannot lie to suspects. The Central Park Five is mentioned in that article and is a blatant example of police lying to coerce testimony and then putting innocent children in prison.
in any other context these tactics themselves would be illegal, and i am firm believer that you can not enforce the law by breaking, and that the police should NEVER how the power to do things the public can not