In Spain, the result of a polygraph is not admitted as evidence in criminal proceedings: no court is required to accept it and it cannot, on its own, prove guilt or innocence. Its real value lies elsewhere —in private and corporate investigation— where it works as a supporting tool, never as a judge. The polygraph records physiological responses (breathing, cardiovascular activity and sweating) while the person answers an agreed questionnaire, and an examiner interprets the charts to estimate the probability that the answers are truthful. With validated techniques its accuracy is around 85-90% according to the American Polygraph Association, but even so it is not infallible and Spanish criminal courts do not treat it as proof. It can accompany a party's expert report or help guide a private matter, but the final assessment always belongs to the judge.
Is the polygraph valid as evidence in a trial in Spain?
In the criminal sphere, no. Spanish case law does not grant the polygraph the status of evidence: a result cannot be used to convict or acquit, among other reasons because it touches on the right not to incriminate oneself and because its reliability is not absolute. In practice, this means that a favourable —or unfavourable— result has no binding weight before a criminal court.
Then what is it useful for?
Its usefulness is real outside criminal proceedings. In the private sphere it helps clear up doubts in a couple or within a family; in the corporate sphere it supports internal investigations into theft, leaks or fraud, always voluntarily. In these contexts the polygraph does not replace anyone's judgement: it provides an objective piece of information to move from suspicion to a reasoned decision.
Can it be brought before a court in any way?
It can be submitted as a party's expert report —documentary evidence provided by one side— but the judge is free to weigh it and, in the criminal field, will not base a ruling on it. It may add context or support another line of investigation, yet it never substitutes for witness evidence, forensic reports or the court's own assessment.
How we handle it at El Polígrafo
At El Polígrafo the test is carried out by Fernando, a polygraph examiner and forensic psychologist, with a Stoelting CPS Pro system and techniques recognised by the American Polygraph Association. We always explain up front what the test can and cannot do —and in criminal matters, what it cannot do is serve as proof. You can see the test step by step before deciding.