The Law on Brain Technologies in Warfare Series – HUMINT, Detainees, and “Brain Fingerprinting”
Editors’ note: This post is an entry in our series on Air Commodore (ret.) William H. Boothby’s book, The Law on Brain Technologies in Warfare published by Elgar International.
As I outlined in a 2024 post, intelligence gathering has taken on an increasingly important role in the conduct of contemporary military operations. Its importance is reflected in Amy Zegart’s statement that “[i]n the twenty-first century, the tip of the spear isn’t a spear. It’s intelligence” (Spies, Lies, and Algorithms, p. 43). Given the clandestine nature of many forms of intelligence gathering, it is perhaps fitting that the legal basis for such activity is almost innocuously tacked onto Article 24 of the 1907 Hague Land Warfare Regulations as “the employment of measures necessary for obtaining information about the enemy and the country are considered permissible.” Those measures include the collection of human intelligence (HUMINT), which is one of a wide range of intelligence categories that extends to categories such as SIGINT (signals intelligence), IMINT (image intelligence), MASINT (measurement and signature intelligence), GEOINT (geospatial intelligence), open-source intelligence (OSINT), CULTINT (cultural intelligence), and even CRIMINT (criminal intelligence).
HUMINT is often thought of primarily in terms of espionage involving human source contact operations. However, it more broadly includes screening the appearance, possessions, and attitudes of persons stopped at checkpoints during cordon and search, and with the handling of detainees, tactical questioning at the point of capture, and the exploitation of captured documents. It also involves: the debriefing of refugees, displaced persons, local civilians and your own forces; liaison operations with host and allied military and civilian authorities; and the interrogation of detainees (2006 Human Intelligence Collector Operations, paras. 1-4 to 1-27). Like many aspects of modern conflict, technological advances have had a significant impact on HUMINT operations. This is most directly through the use of social media to recruit and direct sources, and collect the intelligence they obtain (see here and here).
As Bill Boothby identifies in his recent book, The Law on Brain Technologies in Warfare, there is also scope for using brain-related technology to monitor the thoughts of detained personnel while being interrogated for intelligence purposes. As he identifies, the current technology does not permit mind steering or mind reading. However, it might have a “utility in lie and deception detection and perhaps in revealing subconscious brain information (p. 279-80). The advantage of being able to confirm the veracity of what a detainee is saying is obvious. The scenario Boothby identifies (p. 280) is,
State A uses a BCI [Brain Computer Interface] system to obtain information from combatants from an enemy State B who have been captured during hostilities. The technique that is employed involves the wearing by a prisoner of an external headset. The prisoner is then asked a series of questions and their answers, together with the electrical brain activity as detected.
While sounding futuristic, the capability not only exists, the technological advances in “brain wearables,” which include BCI systems have the potential to significantly reshape the landscape of neurological monitoring. They are making the traditional clinical approach to electroencephalogram (EEG) laboratories appear obsolete (see here, here, and here). Referred to as brain fingerprinting, it is already being used, albeit to a limited degree, by some State law enforcement agencies, in courtrooms and for national security purposes (e.g. India & Singapore). This is being done on the basis that brain scans are less fallible than traditional lie detector tests. It has been suggested to be a game-changing tool that “revolutionizes the way intelligence is collected and judicial prosecution is carried out by significantly speeding up investigations and interrogations.”
The legally preferable way of using brain fingerprinting technology is to obtain the consent of the detainee. Such consent must be freely given. However, the context in which the detention occurs can make that challenging. A legal analysis is likely to turn to whether a detainee lacked the free will to participate in the employment of this technology. Bill Boothby assesses the application of this non-surgical use of technology in terms of potential breaches of international humanitarian law (e.g. prohibitions against torture, abuse, threats, coercion, disadvantageous treatment, outrages upon human dignity, medical experimentation) and international human rights law (e.g. protection against torture, abuse and degrading treatment, being subjected to inhumane treatment, interference with privacy) when used on prisoners of war (POWs).
This post expands Bill Boothby’s analysis by looking first at the broad protections found in Article 17 of Geneva Convention III (GC III) relating to the questioning of POWs; protection not only against physical or mental torture, but also “any other form of coercion … inflicted on prisoners of war to secure from them information of any kind whatever.” The analysis will then turn to the potential use of brain fingerprinting in the investigation of POWs for alleged disciplinary or criminal activity, a situation that could see BCI being used beyond simply intelligence gathering. Finally, the discussion will turn to the application of this technology to unprivileged belligerents and civilians not having POW status, not only during international armed conflict, but also those conflicts “not of an international character.”
Legal Questions and the Use of Brain Fingerprinting
As was established in the 2004 International Court of Justice Wall Case (para. 106) international humanitarian law and/or human rights law may apply during armed conflict. Discussed less is the practical and protective advantage that may result if humanitarian law is applied since it is often more detailed and proscriptive than its human rights law counterpart. The questioning of POWs is one example where not only is coercion prohibited when attempting to gain any information, but the protection extends in Article 17 to not “being threatened, insulted, or exposed to any unpleasant or disadvantageous treatment of any kind.”
Similarly, Article 13 of GC III extends humane treatment to the protection “against acts of violence or intimidation and against insults and public curiosity.” In contrast, the International Covenant of Civil and Political Rights certainly lists essential protections, but the only specific reference to coercion is made in the context of the freedom of religion or belief, and there is no particularized prohibition referring to unpleasant or disadvantageous treatment of any kind. This is one example where, at least for international armed conflict, the specialized international humanitarian law (the ex specialis derogat legi generali) provides an advantage over the more general human rights law.
However, the expansive wording of Articles 13 and 17 is tempered by the meaning of coercion, and the reality that POWs may be investigated or questioned in respect of disciplinary or judicial matters independently of the desire to obtain intelligence. These latter investigations more readily introduce human rights law issues. Coercion has been defined as “the action of making somebody do something that they do not want to do, using force or threatening to use force.” Meanwhile, force is defined as “violent physical action used to obtain or achieve something.” In a 2020 Commentary to GC III, the International Committee of the Red Cross (ICRC) applies a broader interpretation (para. 1824) indicating that “[t]he decisive factor in determining whether coercion has occurred or is occurring is whether the method used deprives or impairs the prisoner of the exercise of free will and autonomy.”
Other Scenarios for the Use of Brain Fingerprinting
Even with the broader ICRC interpretation, there is considerable scope below the threshold of physical violence or scenarios impacting on free will and autonomy to try and obtain information from a POW without breaching humanitarian law. Such tactics are reflected in interrogation techniques such as offering incentives, and the emotional fear-up; emotional fear-down; emotional pride, ego up and ego down; and the emotional love, hate, and futility approaches (Human Intelligence Collector Operations, paras. 8-21 to 8-51). Importantly, such interaction cannot involve threats, insults, or improper treatment.
A POW may be approached to participate in brain fingerprinting in respect of an investigation of disciplinary or judicial matters. In this regard they are subject “to the laws, regulations and orders in force in the armed forces of the Detaining Power” (GC III, art. 82) and trial by a military court unless the domestic law of that power permit trial by a civilian court for a particular offence (GC III, art. 84). Disciplinary matters are generally thought of as minor offences imposed within a detention facility while judicial matters are equated to more criminal proceedings. The use of BCI technology is most likely to be applied in respect of criminal investigations. The investigation of criminal matters could extend to war crimes alleged to have been carried out by the POW prior to capture. These types of investigations raise issues related to the manner in which BCIs are employed and to what veracity standard for criminal versus security intelligence purposes.
In respect of judicial proceedings Article 99 of the GC III specifically states “[n]o moral or physical coercion may be exerted on a prisoner of war in order to induce him to admit himself guilty of the act of which he is accused.” This humanitarian law prohibition is grounded in human rights based norms relating to the voluntariness of statements and ultimately fair trial guarantees. As is evident with the nascent use of brain fingerprinting in a civilian context, this technology could have application to POW related criminal investigations. The application of brain fingerprinting raises issues grounded in human rights law concerning the use of torture, abuse, inhumane treatment, coercion, and undue pressure being brought to bear on the POW. However, standard investigatory techniques may involve the use of emotional and other pressures that do not breach international or domestic human rights norms.
As with polygraph examinations, brain fingerprinting may be used to eliminate suspects, to impeach or corroborate other pieces of evidence, or develop leads even in a POW context. However, the use of polygraph tests in criminal investigations and a screening context has been criticized (see here) and is often rejected by courts dealing with criminal matters as being unreliable (see here). It has been suggested that brain scans are a far less fallible means of separating the guilty from the innocent, with claims that various tests have a 95 to 100 percent accuracy rate. However, lie detection based on EEG results and another approach, functional magnetic resonance imaging (fMRI), has also been challenged by neuroscientists.
The term “brain fingerprinting” may suggest a standard of reliability not matched by the result, as fingerprinting is likely to be seen as more reliable than what is fundamentally “lie detection.” It has been suggested that the use of advanced technology such as artificial intelligence (AI) offers one way to improve the accuracy and reliability of lie detector tests “by facilitating the collection of biometric information, brain activity data, and changes in an examinee’s cardiovascular system.” A fundamental question is the degree to which brain fingerprinting enhances such detection. Ultimately, the attractiveness of being able to uncover deception and its acceptance in the civilian realm will mean BCIs are likely to be applied in a military context during armed conflict as well.
Detention Other Than as POWs
Bill Boothby’s discussion of BCI for the purpose the questioning of detainees is limited to POWs. However, there are other armed conflict related scenarios that point to an even broader application of the technology. One such scenario is occupied territory during an international armed conflict where civilians and members of the armed forces who participate in resistance movements may be detained while not meeting the requirements of law belligerency. The issue is how humanitarian and human rights law protect detainees who do not qualify as POWs. As was outlined in an earlier post, a contemporary example where that may occur is if the Baltic and Scandinavian States must invoke their total defence plans for resisting a potential Russian invasion.
The end of the Second World War saw greater acceptance that members of the armed forces who fail to meet the criteria for lawful belligerency, or civilians who participate in hostilities are unprivileged belligerents who are equated to spies. Unprivileged belligerents can be detained and prosecuted under the domestic law of a detaining power, or the security provisions of Article 64 of the Fourth Geneva Convention (GC IV) dealing with civilians who are “in the hands of a Party to the conflict or Occupying Power of which they are not nationals” (GC IV, art 4). Such criminal proceedings can extend to the prosecution of persons detained for incidents of espionage and sabotage (see GC IV, art. 68). This could result in detaining authorities seeking to use BCI technology in the investigation of such crimes in the same manner as they might use it in a civilian criminal law context.
Since unprivileged belligerents do not have lawful status, they are technically civilians under the binary approach towards categorization that underpins international humanitarian law. Further, there are civilians whose activities do not qualify as unprivileged belligerency. The wide scope for civilian involvement in occupied territory is evident in the 2020 Resistance Operating Concept (p. 26-28), which divides resistance movement organization into underground, auxiliary, guerrilla and public components. With unprivileged belligerency focused on persons engaging in hostile conduct (e.g. direct participation in hostilities), there are also other civilians providing support to the resistance in occupied territory who may be detained and potentially prosecuted under the detaining power’s domestic law. These civilians may be detained for imperative reasons of security, be held in internment camps or assigned residence (see GC IV art. 78) and still be the subject of intelligence gathering efforts or criminal investigations during which the use of BCIs might be considered.
Like for POWs, Article 31 of GC IV states “[n]o physical or moral coercion shall be exercised against protected persons, in particular to obtain information from them or from third parties.” This provision must be applied along with those that require humane treatment and respect for their person (art. 27), and prohibit physical suffering, murder, torture, corporal punishment, mutilation and medical or scientific experiments (art. 32). An ICRC 2025 Commentary to GC IV (paras. 2221 & 2254) indicates detained or interned persons are particularly at risk of being coerced, and that the Article 27 respect for the person extends protection from such coercion to those in assigned residence, internment or detention.
Detained persons who do not qualify as protected persons under the Fourth Geneva Convention would still receive protection from Additional Protocol I (AP I) in conflicts where it applies. An example would be the situation where Russia attacks NATO and it responds militarily, since that Protocol would apply as a matter of law to the conflict for all but two NATO members (i.e. the U.S. and Turkey). Unprivileged belligerents who do not qualify as “protected persons” under the Fourth Geneva Convention (e.g., citizen of an allied State a national not a party to the conflict) would be protected by the fundamental human rights guarantees, including respect for the person found in Article 75 of AP I. In addition, there is also the protections found in international and domestic human rights law applicable in situations where humanitarian law is deficient.
Non-international armed conflict presents a different and, in some ways, a more significant challenge. Counterinsurgency operations are particularly dependent upon being intelligence led. With no protected combatant status for insurgents, it is highly likely that participants will be detained and prosecuted under the domestic law of the territorial State. This would extend to those carrying out espionage on behalf of an insurgent group. Civilian supporters are also subject to detention and prosecution for crimes related to providing support to an organized armed group, or for membership in that group even if it does not extend to direct participation in hostilities.
The questioning of detainees may be carried out not only by military intelligence, but also by police (e.g. Special Branch, U.S. FBI) or counterintelligence agencies (e.g. Israeli Shin Bet, Russian FSB). To the extent that the use of BCIs can be justified as enhancing the veracity of the intelligence or crime related information obtained through questioning its application may be particularly important in a counterinsurgency context. Ukraine has taken extraordinary steps to collect and retain information for use in judicial proceedings regarding potential war crimes by Russian forces in that international armed conflict. However, as was evident in Nigerian efforts to prosecute members of Boko Haram, the collection of evidence on the battlefield generally poses a significant challenge. As this author has noted the ability to obtain such evidence admissible at a criminal proceeding can be the Achilles heel of contemporary efforts to obtain justice. A lack of physical evidence and forensic investigatory capacity often leads to a heavy reliance on confessions, which in turn can raise allegations of detainees having been tortured or abused. Questions whether BCIs have been used in a manner compliant with international humanitarian, or more likely in the case of non-international armed conflict, human rights law, would undoubtedly arise.
The robust humanitarian law framework governing the use of BCIs during international armed conflict for the purposes of questioning both POWs and others is significantly less well developed for its non-international counterpart. There are the general humane treatment obligations found in common Article 3 of four Geneva Conventions, and the human rights guarantees found in Articles 4 (e.g. respect for the person), 5 (e.g. physical or mental health not endangered) or 6 (e.g. not compelled to confess guilt) of Additional Protocol II in situations where it is applicable. Given the domestic nature of the hostilities and potential criminal proceedings, the use of BCIs is most likely subject to human rights protections established under national law, as informed by international human rights that would apply.
Finally, amongst the protections extended in the 1998 Rome Statute to persons under investigation, is protection from being compelled to incriminate themselves, or be subjected to any form of coercion, duress or threat, to torture or to any other form of cruel, inhuman or degrading treatment or punishment (art. 55). This would apply to investigations relating to both international and non-international armed conflicts.
Conclusion
Bill Boothby’s book on the use of brain technologies for information gathering and espionage purposes highlights that their use appears to be very futuristic. In one example he invites the reader to suspend belief (p. 280) as he posits the introduction of an electrode into an enemy commander’s cerebral cortex through its introduction into the bloodstream by an officer having consumed muesli. While having an air of unbelievability it should be noted that Tim Weiner indicates in his controversial 2007 book, Legacy of Ashes: The History of the CIA (p. 482-83) that in the aftermath of 9/11 the assistant director of central intelligence discussed one way a national identity record could be established for Americans was to record thumbprints, blood type, retinal scans, facial pictures, voice prints and DNA on a chip that would be introduced in the bloodstream. It was an approach acknowledged to be like “the KGB, NKVD, Gestapo” and obviously one that never materialized.
However, as the author William Gibson has sagely noted “The future is already here—it’s just not evenly distributed.” The use of BCIs as a form of lie detection for information gathering purposes may reflect the fact “the things that will constitute the normal or everyday within the lives of those living in the future already exist for some today.” Bill Boothby has rightly noted this technology raises significant legal issues concerning individual rights. However, as its use in contemporary legal proceedings indicates, this does not mean the use of BCIs in the form of brain fingerprinting is prohibited. That said, those considering or using such technology must be required to meet the legal standards established in international humanitarian law as well as international and domestic human rights law.
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Ken Watkin served for 33 years in the Canadian Forces, including four years (2006-2010) as the Judge Advocate General.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.
Photo credit: Getty Images via Unsplash+
