Can You Say No to a Lie Detector Test in Singapore? And Other FAQs

Last updated on January 8, 2024

Featured image for the "Can You Say No to a Lie Detector Test in Singapore? And Other FAQs" article. It features a man taking a polygraph test.

A lie detector or polygraph is a machine that attempts to identify when a person is lying. They are commonly used by law enforcement authorities investigating crimes all over the world, including in Singapore. If you are asked to take a polygraph test, here’s what you should know.

How Does a Polygraph Test Work?

The polygraph attempts to detect lies by reference to certain physiological responses, believed to be indicative of lying, such as irregularities in breathing patterns, blood pressure, pulse and skin conductivity. These are measured by hooking the subject up to the machine via various attachments to the chest and one hand and arm.

The polygrapher then asks a series of questions, some of which are relevant to the crime and some of which are merely intended to set a baseline for a true and false result. The subject is asked to lie to an irrelevant question for the latter.

However, there are no specific physiological reactions that can be consistently associated with lying. Different people’s bodies react differently when they lie. Some people’s breathing pattern changes right before they lie, other sweat a little more, some people’s heart rate increases – but others’ do not.

For this reason polygraph tests are known to be wildly unreliable. Innocent but nervous subjects sometimes fail them and guilty but calm subjects sometimes pass them.

How Can a Polygraph Test be Used against Me?

The short answer is, it can’t, at least not as evidence against you in a criminal case.

In Singapore, and indeed in much of the rest of the world, polygraph tests are inadmissible as evidence against an accused person in a criminal case. This is because its inherent unreliability means that evidence of this kind is more likely to simply create confusion and controversy as to its evidential value, rather than actually weigh clearly towards guilt or innocence.

Why Do the Police Use Polygraph Tests?

Even though polygraph tests are inadmissible as evidence in a criminal case, law enforcement agencies still find them useful for deciding whether to recommend prosecution, in cases where they might feel they don’t presently have enough evidence to do so.

Where the police are on the fence about a suspect’s guilt, a failed polygraph test might be enough to make them lean towards recommending prosecution, or at least recommending further investigation, if they feel they have insufficient evidence to secure a conviction.

Conversely, a passed polygraph test might be enough to convince police, in a case where there is little evidence of a person’s guilt, to recommend avoiding wasting further resources on continuing the investigation.

Can Victims be Asked to Take a Polygraph Test?

The police may request any person involved in a case to undergo a polygraph test. Hence, besides accused persons, victims and/or witnesses may be requested to take a polygraph test. Generally, such a test is employed when there are conflicting accounts provided by the persons involved (e.g., “he said, she said” such as in sexual assault/rape cases), and all other investigative leads have been exhausted.

However, according to the Association of Women for Action and Research, questioning victims of sexual offences about highly sensitive and distressing matters is likely to elicit emotional responses and consequently cause the polygraph results to be potentially inaccurate. In 2022, a victim of alleged sexual misconduct said she had to undergo a polygraph test. She claimed that the test can insert doubt into the minds of sexual assault survivors, making them question their true intentions when they were with their abuser.

I’ve Been Asked to Take a Polygraph Test. Should I?

Polygraph tests are voluntary and your written consent is required.

If you are asked to submit to a polygraph test, the good news is that the police clearly haven’t decided to recommend prosecution yet. Whether you should take the test is a big question and one that should be considered in light of all the facts of your case. Therefore, if you find yourself in such a situation, you should say you need time to take legal advice before deciding and then immediately call a criminal lawyer.

This is because your response to the police’s invitation will inevitably affect their assessment of your guilt. For example, if you decide to take the polygraph test:

  • And you pass the test, the police may well conclude that you are innocent and take no further action.
  • But if you fail the test, the police may well conclude that you are guilty and recommend prosecution.

On the other hand, if you decline to take the polygraph test, the police may conclude it is because you are guilty and recommend prosecution. They may also want to record another statement from you about the reasons why you chose to decline taking the polygraph test.

If this happens, you should simply state for the record that your decision to decline the test was based solely on legal advice you received. Because your legal advice is covered by solicitor-client privilege, it is difficult to pry any further than that.

If additional possible reasons for refusing the test are suggested to you, such as you being afraid the test will indicate your guilt, you should simply repeat the sole reason already given (i.e. that your decision to decline was based solely on legal advice you received) and ensure that this is the only reason included in any written statement you sign.

Ultimately, internal police decision-making (on matters such as whether to recommend prosecution) is an opaque and secretive process. It is difficult to identify whether certain decision-making criteria are being applied consistently, or if so, what they are.

That’s why it’s important to seek legal advice from an independent criminal lawyer on this important decision rather than simply trust any verbal assurances from police officers about the likely outcome of your decision.

Can I Volunteer to Take a Polygraph Test?

You certainly can but if you do, you probably won’t be given one unless the police believe it would be helpful to them.

Volunteering to take one would certainly tend to suggest innocence though. Therefore, if you had volunteered to take a polygraph test while being interviewed to prepare your statement, you should ensure that the fact that you have volunteered to take a polygraph test is specifically included in your written statement.

Can I Have My Lawyer Present While I am Taking the Polygraph Test?

The police are under no obligation to allow your lawyer to be present while you take a polygraph and are very unlikely to do so.

However, if you are a child or have an intellectual disability, you should raise this and ask for an appropriate adult to be present.

Can I Choose to Answer Only Some Questions and Not Others?

You have a right against self-incrimination, meaning you are not required to say anything that could suggest that you are guilty of an offence. So in theory, yes, you can choose to answer some questions and not others.

However, you should bear in mind the purpose of the polygraph test. It is not to gather evidence to use against you, as with the statement-taking process. It is just for the police to form an impression of your honesty and innocence.

If you decline to answer some questions during a polygraph, the impression formed of your innocence will certainly be a negative one and you will have failed to achieve the only possible objective you could have in taking the polygraph test: showing that you have nothing to hide.

Therefore if you think you might need to decline to answer any question that is likely to be asked during a polygraph test, you may be better off declining to take the test altogether. You should seek legal advice on this issue if it’s relevant to you.

Can I Get a Copy of the Results of the Polygraph Test?

The police are not legally required to provide you with a copy of the results of the polygraph test. While you can certainly ask for it, they are unlikely to accede to your request. Given that the results are inadmissible in court, they are unlikely to be of much use to you in any case.

While the answers above should be helpful in reaching your decision, there is really no substitute for legal advice on this issue that takes into account your specific circumstances. Remember that any conversation you have with a lawyer about this issue is privileged and you don’t need to tell anyone what was discussed.

Good criminal lawyers can usually make themselves available at short notice to have a short discussion about issues like this by phone. Don’t be afraid to arrange a phone call with one to make sure you are doing everything you can to protect your interests.

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