Why dont the police use lie detectors to see if criminals are telling the truth??

kathy_is_a_nurse

Besides the fact that you can beat a lie detector, the constitution says that a person cannot be forced to incriminate themselves. So they have to volunteer to take the test.

psych_78

Because lie dectectors do not have sound evidence for efficacy!! Despite what Trisha Goddard says lie detectors are not 99.9% accurate. Many factors can affect the outcome of a lie detector, and people can beat the lie dectector by using strategies to either conceal their emotions or to disrupt the whole procedure, making their results unreliable. Lie detectors do not tell whether someone is lying or not - they merely report physiological arousal in response to questions asked.

replybysteve

Because they're not reliable, contrary to what you see on TV.

Lie detectors don't detect lies, they detect things about which a person has concerns.

So, for example, a parent let's their kid out to play and the kid is killed. The parent will feel like they killed the child, and if put on a lie detector and asked, it will read positive. Because they feel responsible.

But lie detectors don't work on serial killers because they are without any remorse or responsibility, they truly don't care. If you ask them "did they kill..." it would not indicate.

Not Ecky Boy

In my day a clip round the earhole got to the truth quickly enough.

kja63

Lie detector tests are fallible. Also, they are not admissible in court. And finally, a person accused of a crime is not required and cannot be made to take one.

Leogirl0804

because lie detectors can be compromised. They are not 100%.

Judge Dredd

They are used in law enforcement, just not often.

d0wnward.spiral

any idiot can pass a lie detector.

ladyinblue

because they are not admissable in court due in part to the fact that they do not always work

McClean

Why hasn't anybody stated the obvious here...they do use lie detectors. Frequently. They can't compel people to sit a polygraph but it's often used to eliminate suspects etc.

Jackie H

Probably because they are not 100% reliable as people can beat them.

joeanonymous

Police do use polygraphs to see if criminals are telling the truth, they use them to determine if they are being deceptive when making certain statements.
There are drawback to using this technique for large numbers of people.
Polygraph tests take an average of 3 hours to complete for each one. The results only show that the person may or not be being deceptive. There is no flashing red light for "lie" and a green one for "truth". The results cannot be used in court (here in Canada) and if the only evidence you have is a polygraph test that says the person is being deceptive and the person is denying guilt, then you won't get a conviction.
Polygraph techs. must take a long and expensive training course and many smaller police services do not have the resource to dedicate a police officer full time for this job. We only have one polygraph technician who is also a detective. He is responsible for his own investigations and tries to squeeze in polygraph request whenever possible.
Polygraphs are generally used as a last resort technique by many officers, especially if you get a situation where two people may be responsible for a crime and you don't have enough evidence to pin point one over the other. Polygraph tests usually include some kind of interview/interrogation after-wards and sometimes people will admit their guilt when confronted with the polygraph results.

jurydoc

I find it fascinating that in most of these answers comments are made about the "lie detector" not being 100% accurate. Interesting that polygraphs (the actual name for the test) have been found to be at least as accurate, if not moreso, than eyewitness testimony which we routinely rely upon in a court of law with very little question. I would much prefer to rely on a well-administered polygraph examination by a qualified examiner than eyewitness recall any day.

mick271602

because they are not 100% reliable...... a bit like contraception.

lonewolf1

They are not 100% accurate, and can be beaten, plus in many states, the results of a lie detector test is not admissible in court, for or against you.

Studbolt Slickrock

Lie detectors are a bunch of crap.

James Mack

Because they are not accurate and hence not admissible in a UK court. Standards of course are a lot lower in the US.

NONAME

They cannot be used as evidence for a case.

They're more of a fear tactic to get you to admit to the crime. They are pretty pointless these days since everyone knows they are not submittable in court. If we were to think that they are, then we'll tremble in fear before the test and hopefully admit to the crime.

Alfred E. Newman

they arent 100 % accurate,some people can beat them.

Silly

lie detectors dont always work

420

Because the results of the lie detector cannot be used as evidence in court as lie detectors are unreliable.

keepmynameoutchamouth

Because they can be inaccurate and therefore ineffective.

Also, when people are forced to take polygraph tests, there is a 50:50 chance the results will be inconclusive, false positve, etc.

majorbratchat

its an infringement of human rights apparently!

kveryeffective

Lie detectors don't work.

twysty

They are not admissable in court

wicked_lette_4_lyfe

that would b 2 easy. & if its a perfect criminal then they have perfected how 2 lie so the lie detector thinks they r tellin da truth

Mujer Bonita

B/c the evidence doesn't count in courts. It's not admissible or whatever.

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