Law Enforcement/criminal testing

The Polygraph and the Investigator/Field Officer
“POLYGRAPH”-Originated from the Greek word poly meaning “many” and graphos meaning “writings”. “For every lie, there is a shred of truth-that is what makes it seem to ring true” Author Unknown. The Polygraph examination is also known as Psycho physiological Detection of Deception or PPDD.

Polygraphs, commonly and erroneously called “lie detectors”, are scientific diagnostic instruments that monitor and record a person’s physiological reaction to psychological threats.

Polygraph exams do not, as their misleading nickname suggests, detect lies. They can only help in the detection of whether deceptive behavior is being displayed. The instrument records changes in a person’s heart rate, blood pressure, respiratory rate and electro-dermal activity among other things. The polygraphist then uses methods developed from decades of validated scientific studies to analyze this data. Results of a polygraph will often only be as good as the investigation leading up to it. If and when a polygraph should be used, will vary from case to case but in no circumstance should it be used as a last resort.

If possible, the polygraphist should be consulted early on in a case as to pre-test investigation recommendations. The polygraph is not a substitute for a proper investigation but the more closely the polygraphist and the investigator work together the more successful they will be. Prior to the polygraph test, the investigator, during his/her investigation should try to withhold from ALL suspects at least three case facts in which normally an innocent person would NOT know about the case. Examples are: details of exactly what was stolen, points of entry and exit, tools left behind, weapons used or anything unusual about the crime scene. The investigator must then provide the polygraphist with accurate and complete case facts at least 24 hours before any polygraph exam and prepare the suspect for the examination. The basic process surrounding the Polygraph Examination The polygraph examination will take approximately two to three hours. This depends on the issues and the person being tested. There will be a pre-test interview, the actual test and then a post test interview or interrogation if warranted. The obvious objective is to determine if the suspect is telling the truth. This will help the investigator determine the next step he/she should take in their investigation. If the suspect’s test results indicate deception, the polygraphist’s objective then is to obtain a court admissible confession. If this objective is successful, the primary investigator should be available at this point to transition the confession to him or her. A suspect’s mental and physical conditions are critical, as they will affect the test. Consequently, there may be times when the examination will have to be postponed for another time. Polygraphs will not be performed on suspects under the following conditions:
Heart conditions without a doctor’s note.
Pregnant women.
Juveniles without signed permission form from at least one parent/guardian or court order from juvenile court judge.
Any suspect being forced to take the test.
Anyone who refuses to sign the permission form.
Anyone who has already been formally charged unless a Polygraph Agreement and Stipulation has been properly signed.
A suspect who has already been tested by another law-enforcement agency.
On suspects in cases when an officer’s conduct is in question.
Suspects can possibly be tested even if they suffer from mental or physical conditions such as addictions, bipolar etc … Consult with the polygraphist.

The investigator should only ask a suspect to take a polygraph test if the investigator intends to follow through. Never bluff.
The investigator should never consider a suspect to be truthful if they agree to a test. In criminal investigations, over 50% of law enforcement polygraph examinees are found to be lying. Only one crime/issue (the most serious) will be covered during anyone-polygraph exam. If the investigator wants another crime or aspect of it examined, it will have to be done at a later date. If a suspect confesses to a repeatable crime (i.e. burglaries) before the polygraph exam has been conducted, they should still be tested for the extent of their criminality. They may be trying to hide evidence of
prior more serious crimes.

The investigator will not interrogate the suspect on the day of his examination. As a matter of fact, when a suspect agrees to take an exam, all interrogations should cease at that point.
Examples of positive approaches in getting a suspect to take the polygraph examination:

Since no one can be forced to take a polygraph examination, it is important for the investigator to use a positive approach in convincing the suspect to take the test.

Some wording suggestions include: ‘The facts indicate that you’re involved, but you claim you are not. The best way to settle this is for you to take a polygraph examination.” “We call it a truth verifier. That is, if you are telling the truth, it will show that you are innocent. Every month the polygraphist clears many innocent people.” “Taking the examination must be of your own free will. If you want it, we’ll be happy to give it to you. You do want to prove your innocence don’t you?”

Another example … “You claim that you are telling me the truth. Are you willing to prove to me that you are telling the truth? Great! I am glad you are willing to prove your innocents and taking a polygraph exam will verify you are telling the truth. Since you are telling the truth, then you are willing to take it aren’t you?” The investigator should note the suspect’s reaction when asked about the polygraph exam so they can inform the polygraphist when also giving case facts. Did the suspect hesitate, claim it isn’t court accepted, or did the suspect act pleased to have the opportunity to clear them self. If the suspect refuses, don’t make an immediate assumption that they are guilty. Sometimes suspects are afraid because of unrelated crimes that may be revealed or they just may fear the process itself. Point out that the polygraphist will only ask specific questions about that one particular crime. That there will be no surprise questions and that they have the right to refuse to answer any question they so desire. If the suspect still refuses, ask them “Why?” If they give an answer that makes little or no sense, resume your interrogation, because there is a 95% probability that they are lying about some aspect of the crime under investigation. If the suspect agrees to take a polygraph, they should be notified, generally, a day in advance of the test. If possible they should come to the polygraph suite by their self. Of course other arrangements should be made if the suspect does not have transportation. They should be told to do things they would normally do such as taking medication, meals, etc … These plans can be arranged with the polygraphist prior to asking the suspect to take the exam. The case should have been reviewed with the polygraphist prior to the test date. At least one half hour before the appointment with the suspect, the primary investigator should arrive with all pertinent case information to include background information if applicable, such as prior criminal records especially for similar crimes, motives, financial status, religion and faithfulness, and anything else that the investigator may think of value on each person being tested.

If the suspect changes their mind after they are scheduled for a test, the investigator should still attempt to get them to personally come to the polygraph suite. Tell them: “You need to personally cancel the appointment with the polygraphist, since you had your appointment with him”. I, as the polygraphist, will try to alleviate their fears and get them to take the test. Polygraph has other applications besides testing suspects for criminal involvement. It can be used to test for hidden illegal assets and the truthfulness of witnesses among other things. The polygraph is another tool at the disposal of the investigator. With it, the innocent can be more quickly cleared, the deceptive exposed and potentially more confessions gained.

If you have any questions or need any more information about polygraph, please feel free to contact Allied Polygraph at 302-907-9969 or,

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