Edit: For an example of a final address that was considered not to reverse the onus of proof, where an accused’s responses were described as “guarded” and “deficient”, see Cummins J’s reasons in DPP v Baker(No 3).
And the position of closing addresses that refer to lies as consciousness of guilt (as expressed in Edwards v R (1993) 178 CLR 193) allows the prosecution a much wider lattitude to critique the responses of an accused. In R v McCann  QCA 289 the Queensland Court of Appeal related the following, without disapproval:
 In the course of his address, counsel for the prosecution referred to the lies constituted by the appellant’s initial claim that he had no knowledge of the matter and had not been at the complainant’s home and had not had sexual relations with her:
“Think about the lies, the lies that he told. What would you do if you were an innocent man and two cops rock up at your door at 6 a.m. in the morning, or 6.30, or whenever it was. They come to your door and they are effectively – they’re telling you, ‘Look, there’s been a sexual assault and we think it might have been you.’ Now, they’re accusing you of a very, very, very serious crime. Would you lie to them out of fear that your girlfriend might find out? Did he think the police were going to run over and tell his girlfriend that, you know, he’d had sex with this other woman? It’s just ridiculous. Or would you think to yourself, ‘I better straighten this out really, really, really quickly. If I don’t I could be going to gaol here. I’ve got serious, serious problems and I’ve got nothing to hide. I know I’m innocent, I’ve got nothing to hide, I’m just going to tell them everything I know and I’m going to straighten this out right now.’ You’d be thinking, ‘I’ve got bigger problems right now than what my girlfriend is going to think.’ ”
“Then he says – rambles about he didn’t want his girlfriend to know, pissed as a nit. He needed to get his story straight quickly and stick to it but he wasn’t smart enough to do it. You can just – on the tape you can just hear his mind slowly ticking over. You can tell he’s making it up as he goes along. He changes his story multiple times. If you were innocent, if you were in that situation, you had nothing to hide, would you do that? Can you imagine yourself on the tape, trying to spin these yarns like that if you were innocent?” 
While such rhetoric would need to be balanced by appropriate jury directions by the presiding judge, no objection was taken to this approach by counsel or criticism made of it by either court.
Some cross-examination questions have no place outside TV drama.
The recent case of R v Mallia  VSCA 175 discusses the limitation on the prosecution asking questions of defence witnesses like, “Who else but you would have done it?” or, “Why would the other witness lie?”
Referring to Palmer v The Queen (1998) 193 CLR 1, Buchanan JA reiterated why it’s considered unfair to ask an accused to explain the motives of other parties in a case (in addition to the evidentiary rules against opinion and speculation),
9 The principal vice in asking a witness, and particularly the accused, why another witness would lie is the fact that the witness has no knowledge of any matter from which a motive to lie might be inferred is generally quite irrelevant and inappropriately focuses attention on an immaterial and manufactured conflict. To ask an accused why a witness would lie is to invite the jury to accept the evidence of the witness unless a positive answer to the question is given by the accused. The same result might ensue if the prosecutor asks the jury the same question rhetorically.
Questions like these can suggest a reversal of the onus of proof, by making it appear as though the accused is under an obligation to explain or disprove the prosecution’s case. According to the famous Woolmington v DPP  AC 462 and often repeated in Australian law, the duty remains on the prosecution to prove all elements of the charges beyond reasonable doubt, from first to last (other than exceptions, like mental impairment or other specific statutory provisions, that reverse the presumption). The correct view is that absence of proof of motive is entirely neutral: Palmer, at 9. Despite contrary proposals a prohibition on the topic at trial has been maintained by the courts. Questions to witnesses or statements to a jury which invite such speculation can, and do, lead to the quashing of a conviction.
Some references to the possibility of rejecting the accused’s account by the prosecutor are allowable, though. In Mallia, the applicant was alleged to have lured a much younger person who was previously unknown to them to their home with the offer of drugs, then sexually assaulted her. The accused denied offering the complainant drugs. In his closing, the prosecutor (rhetorically) asked the jury, “Why would the complainant leave her friends in the city and accompany the applicant to his home?” and stated to the jury that the applicant had advanced no reason for the complainant’s leaving her friends and going with the applicant.
10 In my opinion, the authorities dealing with the problems created by challenging an accused to explain why a complainant should lie do not preclude a prosecutor pointing out the absence of any explanation for a witness’s conduct other than the motive stated by the witness. The prosecutor in this case did no more than emphasise the consistency and credibility of the complainant’s account by urging the jury to accept the reason advanced by the complainant. I do not think that the prosecutor’s rhetorical question reversed the onus of proof or diverted the jury by raising an irrelevant issue. The prosecutor was presenting an argument which did address the probability of the complainant accompanying the applicant for the reason she stated.
Though not argued, it may be that Mallia has more thematically in common with Weissensteiner v R 178 CLR 217 than with Palmer v The Queen. Logically, the fact that only one version of events is before a court may make it easier for a court to accept that version.
One thought on “"Why would they lie?"”
“Despite contrary proposals a prohibition on the topic at trial has been maintained by the courts.” But only Australian courts. The New Zealanders, for instance, outright rejected Palmer in T v R (1998, NZCA) and the UK and Canada allow the question to be asked with caution. The best evidence law judge ever to sit on the High Court, McHugh J, compellingly dissented in Palmer itself.Not all courts confine Palmer as sensibly as the VCA did in Mallia. For instance, in R v Russo  VSCA 206, the VCA overturned a murder conviction because the prosecutor posed the rhetorical question to the jury: 'if it were not the accused man, then who was it?'! And, in Queensland, when police asked a suspect why a child would allege that he abused her, a trial judge held that the answer 'Because it's true. No I'm not fucking proud of myself' was inadmissible because of Palmer! Fortunately, that stupidity was overruled on appeal:  QCA 284.Everyone agrees that the question 'Why would the complainant lie?' is a dangerous one. But the High Court's Palmer judgment, a classic instance of lazy reasoning by the Brennan court, is equally dangerous.