There is some general confusion about the role of polygraph examinations in criminal cases. Let’s cover some basics. Polygraphs examination results are not admissible in a criminal trial. There was one really bad appellate opinion that seemed to open the door to that possibility, but it was reconsidered. So passing a polygraph really doesn’t help you in a criminal trial.
Polygraphs can not detect if someone is lying. Instead they monitor blood pressure, pulse, respiration etc. The idea is that when you lie you body has a stress response that can be measured as “deception”. However, there are a lot of reasons someone could have these exact same symptoms while telling the truth.
So why take one?
You shouldn’t (at least not without a defense lawyer present), and if you are speaking with a detective about a criminal offense, you must hire a lawyer immediately. Polygraphs can be a set up to get you to confess, a ploy used to trick you into walking into the police station without a lawyer to help you.
Here is a typical situation in which a polygraph is offered by a detective. Suspect Bill is accused of indecently touching a child. There is no physical evidence, but the child made a statement to a relative. The police know this case is weak without a statement, so under the guise of “getting your side of the story” they might ask for a polygraph to “clear you of these allegations.”
Post arrest polygraphs can also be used by prosecutors to help dump shit cases. If the police arrest someone on a serious charge with flimsy evidence, a prosecutor might want the defendant to pass a polygraph so the prosecutor can then reject the case while minimizing anger from the family of the complaining witness. Grand juries are also utilized for a similar function when prosecutors work to get a case no-billed.
Detective use polygraphs as a way to interrogate you
Here is the deal folks, you will never change a detective’s mind about your guilt or innocence by giving a statement, or taking a polygraph. Confirmation bias is real, if a detective goes into your interview thinking you did it, no matter what you say they will still think you did it. Same with a polygraph. So what’s the point? To get you to confess. How do they do that? Here is a typical scenario.
A detective calls and tells you that you are being accused of sexual assault, but they you to take a polygraph to help clear you. So you show up and they strap you in to the polygraph machine. The detective reminds you that you are here voluntarily and can leave at any time (they do this to avoid reading you your Miranda rights). Then you answer some questions. The detective gets upset and tells you that you either failed the polygraph, or the results are inconclusive. The detective says he knows you are lying or holding something back, and if you do not tell him the truth he will tell the judge and prosecutor that you lied. The detective will then tell you that only by telling the truth now can you help yourself.
Think about what a great move this is for detectives; they get a suspect to walk into their office without a lawyer. They strap the suspect to a machine, then claim the machine says they are not being honest and then ramp up the pressure on the suspect, all while telling him he is free to go.
Don’t be a victim of a fake polygraph. NEVER agreed to a interview or polygraph without a defense lawyer representing you.