Lie detector or polygraph testing has long held a compelling allure for those who work with managing sexual risk but, at the same time, the complication remains that we cannot know for sure who we can trust or what that person is really thinking. 

Lie detector evidence has never been considered sufficiently reliable to be admissible in British criminal law cases. However, the use of the lie detector in managing suspects and offenders in the community has been quietly going on for some years. This is especially so for sex offenders, albeit by only a handful of police and probation regions. Extensive research from the University of Kent published in early 2020 concluded that the use of the polygraph is effective for sex offenders and should be used much more widely. The Domestic Abuse Bill of 2020 proposed a pilot scheme to make the lie detector test mandatory for people convicted of more serious Domestic Violence crimes, and this legislation is now making its way through Parliament towards an enacted reality.

Recently, we have experienced Police submitting applications for sexual offenders to be required to co-operate with polygraph testing, as part of a Sexual Harm Prevention Order. Offenders are prohibited from refusing to take a polygraph test on pain of a prison sentence of up to 5 years.

Lie detector or polygraph tests are not being used to detect or solve crimes. This might seem odd, but the lie detector is used to help the police or probation service manage the risk that a suspect or offender might pose whilst in the community. For example, they want to know the truth about whether someone is really having contact with children behind their backs, or is thinking about child abuse.  Many sex offenders have special orders restricting movement or use of the internet, and the police want to know if they are sticking to them. This information is known as a Risk Relevant Disclosure and the police can then take whatever action is appropriate. They are trying to keep the public safe.

Equally, police are not particularly relying on the results of the lie detector. Rather, they mostly rely on what the subject tells them before or after the test. Thus, the police can rely on what the subject admits is their risk relevant behaviour rather than what the test ‘proves’. However, all of the research shows that the number of Risk Relevant Disclosures massively increases when lie detectors will be or have been used. In the face of the test, many confess, and this is the key to its usefulness.

Polygraph testing may be controversial in some quarters but it is not some bogus science. There are strict and complex codes of practice and an examiner must undergo extensive training. Such are the demands of the job that research recommends that examiners do the job exclusively. Most best practice has been imported from America, where polygraph testing is much more established and regulated. Advocates of the polygraph claim very high accuracy, upwards of 85% and often upwards of 95%, although there is good reason the evidence remains inadmissible in criminal court trials. It only ever forms one part of a range of available management tools.

The procedure of a lie detector test lasts several hours. There will be a pre-test phase during which the examiner will gather the subject’s version of the facts regarding the single issue in question. They will formulate together the questions to be asked during the test. After calibrating the equipment to the person being tested, the polygraph testing will begin. The subject will be asked the agreed series of questions typically 3 or 4 times. In the post-test phase the results will be analysed and the subject will usually be told about them then and there. The analysis of polygraph test results is a specialist topic, with results falling into the categories of indicative of deception, not indicative of deception, or (occasionally) inconclusive.

The polygraph examination itself involves measuring the cardiovascular, respiratory and electrodermal systems. The sensors comprise a blood pressure cuff on the arm, rubber tubes on the chest and abdomen and two small metal plates on the fingers of one hand. The actual test usually lasts 15-20 minutes

Nonetheless, the lie detector remains controversial, especially when used with suspects who have not been convicted of any crime, even if they have admitted offending.

Some worry about the quality of the process itself, the regulation and scrutiny of which remains relatively low, whilst others worry about the apparent lack of trust between offender manager and offender.  Additionally, there are concerns around the principle of requiring people (whether mandatory or through perceived consequences of not volunteering) to talk and answer questions when our democracy and criminal justice system (based on centuries of carefully developed legal process) profoundly protects the rights of an individual to remain silent. Some worry about the cost and resource implications. Some worry that it may reward the most sophisticated offenders who can ‘beat the test’.

Others will very much welcome another tool in the battle to keep society, and especially children, safe from sex offenders. It is clear that the officers who use polygraphs consider it a valuable tool.  Some ex-offenders welcome the chance to ‘prove’ they are safe (though the research indicates that police give greater importance to tests indicating deception). Polygraph testing in social services investigations is largely unexplored territory but potentially offers a useful tool to social workers. Criminal Courts might start considering evidence from polygraph tests in relation to sentencing, perhaps supporting a submission that an offender can be safely managed in the community. It would be interesting, for example, as a defence practitioner to meet an application for an SHPO to include polygraph testing, when a pre-existing polygraph test evidences that such an order be unnecessary.

The apparent effectiveness of polygraph testing in substantially increasing Risk Relevant Disclosures is relative to similar groups of offenders who have not been tested. None of the research appears to have distinguished those who have undertaken a therapeutic treatment program, particularly those who have had a psychologically informed one-to-one intervention. This may be important, because such interventions focus on the drivers or causes of offending, against a deep understanding of risk factors and treatment need.

Perhaps the biggest criticism of polygraph testing is that there is little evidence that it reduces risk or reduces reoffending. Although intuitively a Risk Relevant Disclosure seems helpful, this assumes that an officer’s assessment or knowledge of risk factors bears scrutiny. For example, on conviction Sexual Harm Prevention Orders are handed out almost routinely by courts and the terms, though notionally bespoke, are typically boilerplate and very often have little to do with risk the offender presents. So, breach of such an order may be risk related, but still has little to do with sexual reoffending. There is also the question of what, if anything, an officer does with a Risk Relevant Disclosure.

For the cost to be justified, there should to be good evidence that lie detectors reduce offending. It is worth noting that the UK has one of the most onerous and substantial sex offender management schemes in the world, and yet our re-offending rates do not appear to be better than in countries who take a different approach. The UK’s record of using effective interventions remains significantly tainted by the Sex Offender Treatment Program scandal. Lie detectors make good headlines. If the same money were spent on effective treatment, might there be fewer future victims?

In conclusion, polygraph testing is a useful tool in the armoury of law enforcement officers. There is a compelling case for expanding the use of polygraph testing for convicted sex offenders. The process is useful because subjects confess readily to risky behaviours. There is perhaps more to be done to relax supervision of those who ‘pass’ the test so that more resource can be devoted to those perceived to be of higher t risk Moreover, polygraph testing should not be seen as either a panacea or even a scientifically reassuring answer to the risk posed by convicted sex offenders in the community. To effectively reduce reoffending, we must do more to understand the drivers and risk factors for individual offenders and tackle those causes. The research on the effectiveness of lie detectors appears to show that we are not doing nearly enough on this front. 

Matthew Graham is a specialist solicitor and head of the Crime Team at Stone King. Matthew has extensive experience in the field of sexual offending and safeguarding.