Investigation and lie detectors.

Why when the cops, fbi, detectives etc.
Want to know if a suspect really killed a victem
Why dont they just do a lie detector test & ask them if they killed someone ?
I've always wondered about that...
Isent it easier ?

there are methods that lie detectors can be fooled so they need real evidence.

Firstly, it would violate the 5th Amendment to the Constitution to do that (assuming you're in the US).

Secondly, lie detector tests don't actually work very well. They're easy to pass if you know how, and they result in a lot of false positives. The problem is, they don't actually detect if you're lying, they only detect if you're stressed.

lie detector tests aren't incredibly accurate.. it basically measures fluctuations in blood pressure and heart rate, which are supposed to raise when you tell a lie. but if you're messed up mentally (like most criminals), blood pressure and heart rate don't raise when telling a lie. psychologists say it's because bad criminals don't have a conscious, therefore they can easily pass polygraph tests.

like the people said above, they need hard evidence, not just some polygraph which half time is wrong.

haha k.
cause im like watching a&e
and these investigators do ANYTHING to slove a mystery.
but yeah thats true haha thanks.

Like others have said, polygraph tests are not effective at detecting lies.

The police can not force you to take a polygraph test. It is generally not in your best interest to take this test if you are suspected of a crime. Most employers can not force you to take a polygraph test either.

I've never been asked to take a polygraph test but my ex was asked. The first time she worked at a Burger King After a theft the manager said all the workers would have to take a polygraph test. The employees got together and decided amongst themselves that nobody would take the test unless the manager also took the test. When they told him their decision he opted not to have polygraph tests. The second time was when she worked as a custodian at a state university. $300 was taken from a broken change machine and even though nearly anyone could have taken the money they decided to give polygraph tests to the custodians. Instead of all the custodians being asked to take the test the manager decided to only test employees he was suspicious of which turned out to be all the black employees. My ex found out that there actually was a employee union for state workers in Texas and called them. The lawyer for the union said that what the boss was trying to do was illegal and made a few phone calls and it was dropped though one custodian volunteered to take the polygraph test to 'prove' his innocence but he failed the test and instead of having a cloud of suspicion hanging over him he got another job.