As a student studying law at university, one of the daily pleasures which this writer used to indulge in was the watching of Jerry Springer-esque shows, which traded on shock value and voyeurism. One of the recurring themes of the afternoon talk show was the use of polygraph machines to ascertain whether or not a person had cheated on their partner – which they did more often than not – resulting in the failure of the test by the love rat, therefore, shocking everyone involved. The use of polygraph machines is also a feature of nightly current affairs shows here in Australia, and is often cited by the purveyors of such instruments as almost infallible, but is it really? Well, that question is ultimately for other people to answer, because we here at FindLaw are more interested in the legalities surrounding a lie detector test, and whether evidence gained from a polygraph machine is admissible under Australian law.
How does a lie detector test work?
Polygraph machines generally work either by measuring the physiological reactions of a person under question, or by measuring the levels of stress and vibration that can be detected in a person’s voice. The conclusions of a polygraph are deciphered from changes in pulse rate, blood pressure or any muscular activity if the machine measures physiological actions. On the other hand, if the machine measures a person’s voice, then the level of stress in the voice will be the determining factor, and an evaluation will then be carried out by an examiner as to how truthful a person has been.
Is evidence from a lie detector test admissible in court?
The admissibility of evidence derived from a polygraph machine is generally not considered valid by Australian courts.
In R v Murray, Sinclair DCJ in the District Court of New South Wales, set out the reasons as to why polygraph evidence was inadmissible after the accused sought to call on the operator of a polygraph machine to validate that his denials to the charges were correct after taking a lie detector test.
His Honour stated that the polygraph operator’s testimony was not valid because:
• his expression of an opinion as to the facts of the issue, should be within the province of the jury to determine on the facts, presented to them by witnesses who perceived them by the exercise of their physical senses
• the witness was not a qualified expert, but rather an operator and assessor of a polygraph machine
• devoid of any scientific basis, the evidence of the polygraph operator was considered as hearsay, with no probative value.
To further illustrate the point, we can look to s 6(1) of the Lie Detectors Act of New South Wales which states, that any evidence adduced from a polygraph machine will be considered as inadmissible by the courts.
It should be highlighted, that although evidence obtained from a polygraph machine is for the most part inadmissible, this does not however prevent the police from potentially using polygraph tests in the course of their investigations.