top of page

Discretionary and Mandatory Exclusions

Rules of Evidence

Evidence Obtained Improperly or Illegally

Any evidence which was obtained in a manner that contravenes any Australian law, or by ‘improper’ means, may be deemed inadmissible under section 138. Also disallowed potentially is evidence obtained ‘in consequence of an impropriety or contravention of an Australian law.’ Inadmissibility is not automatic, but follows consideration as to whether reasons for admitting it outweigh the reasons against, given the manner in which it was obtained.


Specific rules exist in sub-section 2 in relation to evidence of admissions where an admission is deemed to have been obtained improperly if any of two things occurred during questioning of a person:







Impropriety includes the conduct described in sub-section 2. Impropriety is further defined in s 139, which relates to police procedures and is of no relevance to civilian law enforcers. It is not open to courts to import whole new concepts into the definition of statutory wording when there is sufficient material to establish a clearly defined range of meanings. Because there is nothing to suggest that courts can stretch the meaning of impropriety to include the moral standards or preconceptions of the presiding judicial officer, it is not anticipated that courts will take any sort of expansive view of what amounts to impropriety.


Courts do permit a certain amount of trickery and subterfuge on the part of police. This is especially so when dealing with the technique of a fake gang comprised of undercover police who coax a suspect into confessing to a past crime thinking he will be allowed into a lucrative gang membership or escape the spectre of a re-opened police investigation. Courts have for a long time ruled against forms of pressure and deception that affect the suspect’s ability to give evidence voluntarily[1] but that is as far as they have gone with police.

Nevertheless in Waverley Council v Tovir Investments[2] evidence obtained through undercover surveillance by a private investigator in a residential premises was ruled to have been obtained improperly. An investigator was contracted by Waverley Council to obtain evidence of the use of certain allegedly residential properties were being used as backpackers’ hostels. The method to be used was to pose undercover as a backpacker seeking accommodation while filming the events covertly. The reasons for the ruling included factors that raise suspicion of an attempt by the Council to circumvent existing laws that would prevent them from obtaining the same evidence, but the fact of undercover operations also had some effect. Factors on the side of propriety related mostly to the need to enforce obedience to a court order. It was also considered that any breach of law was inadvertent rather than deliberate. On balance it was ruled to be improperly obtained but was admitted due to its probative value. For detailed reasons, see the judgement, paragraphs 74 to 77. It appears that this judgment applies a highly expansive reading of sub-section 2, paragraph b (quoted above) which makes pretext-based investigations improper, and potentially pointless.


Sub-section 3 lists a range of matters that the court can have regard to when determining admissibility. The list is not exclusive. These include, among others, the probative value of the evidence and its importance to the matter, the nature of the issues in question, the difficulty of obtaining evidence other ways, and the gravity and intentionality of the contravention or impropriety.


Investigators need to be aware that if a law was broken in the course of obtaining evidence, then the evidence is of no benefit. Therefore any risk of legal action or prosecution incurred in the course of an enquiry, which might otherwise be thought worthwhile for the sake of the client, is likely to yield no benefit. A civilian person investigating a criminal matter may, due to the likely gravity of the matter and the fact of them acting alone, be able to persuade a court that it is desirable to indulge a minor infraction. However, a civil matter is not often as serious and a court therefore may be resistant to allowing evidence obtained in conflict with s 138.

[1] McDermott v R (1948) Unreported, HCA, Dixon J, 23 Aug & 22 Sept 1948.

[2] Waverley Council v Tovir Investments Pty Ltd and Rappaport (No 2) [2013] NSWLEC 21.

All statutory sections from unspecified Acts, are sections from a model Act of the Commonwealth Parliament as described on the first page of this chapter, and should be replicated as described in each of the related Acts of each State and Territory. (Jurisdiction to regulate the rules of evidence exists in the States and Territories and not in the Commonwealth).

(a) Anything was done or omitted during questioning which the questioner ought to have known was likely to impair the ability of the person being questioned, to respond rationally;

(b) A false statement was made during questioning which the questioner ought to have known was likely to elicit an admission.

bottom of page