Lawyer Inês de Oliveira Soares, recently awarded for research in this area, supports this hypothesis. She points to the P-300 test as a potentially useful tool for determining if a suspect retains specific biographical memories of the crime.

The test measures the brain's electrical activity with scalp electrodes, capturing automatic cognitive responses when the subject sees visual stimuli related to the investigation.

In the McCann case, the suspect would see strategic photographs of the apartment, suspected vehicles, and possible hiding places. If the person recognises the elements, the P-300 brainwave is activated involuntarily. This suggests their brain contains information consistent with the facts under investigation.

This method’s advantage over the polygraph is that it does not require a verbal response or cooperation from the defendant. The neurological response is immediate and uncontrollable, rendering conscious manipulation impossible.

This memory mapping technique already exists in international justice

In Spain, the test was decisive in the “Ricla” case, involving the disappearance and alleged murder of a woman in 2012.

In India, the court used the same methodology in Adati Sharma’s trial. Sharma was accused of poisoning her ex-husband with arsenic. The neurological exam proved the defendant had detailed “practical knowledge” about handling the toxic substance, which served as the basis for the conviction.

Difficulties in the Madeleine McCann case

Applying this mechanism to the McCann case faces a major technical obstacle. The trial has received extensive coverage for almost two decades.

Much of the investigation’s images and details are public knowledge. The brain of any ordinary person could activate the P-300 wave simply through familiarity with the media.

To overcome this limitation, Inês de Oliveira Soares says the stimuli must use "confidential information." These are crucial crime details known only to investigation teams and the true culprit.

Besides technical challenges, introducing the P-300 test in Portugal faces tough legal and constitutional constraints.

Portugal’s forced use of examinations that extract data from the subconscious conflicts with fundamental rights. These include the right to moral integrity, privacy, and the principle against self-incrimination.

The expert argues that forcing a defendant to undergo this examination would violate defence guarantees. The situation changes if the suspect voluntarily decides to take the test to prove their innocence.