Witnesses — not called
No comment should be made as to the failure of the defence to call a witness who might have been able to assist the defence: Dyers v The Queen (2002) 210 CLR 285. If any comment is to be given it is that the jury should not speculate about what a witness not called might have said: Dyers at .
In Mahmood v Western Australia (2008) 232 CLR 397 at  the High Court held that in a criminal trial:
… where a witness, who might have been expected to be called and to give evidence on a matter, is not called by the prosecution, the question is not whether the jury may properly reach conclusions about issues of fact but whether, in the circumstances, they should entertain a reasonable doubt about the guilt of the accused.
See also Louizos v R, R v Louizos (2009) 194 A Crim R 223 at .
[4-375] Suggested comment — witness not called by prosecution
You have heard that [name of witness] has not been called by the Crown to give evidence. You can take the fact that there was no evidence from that witness into account when you decide whether the Crown has proved the guilt of the accused.
I am not inviting you to guess what [name of witness] would have said if [he/she] had been called. You must not do that at all. But in a criminal trial, where the Crown must prove that the accused is guilty beyond reasonable doubt, a jury is entitled to take into account that there was no evidence from a particular person in deciding whether or not there is a reasonable doubt about the accused’s guilt … [refer to the submissions of the defence and Crown on the issue].
[4-377] Suggested direction — complainant not called on retrial
The appropriate direction to be given where a complainant did not give evidence in person in accordance with s 306B Criminal Procedure Act 1986 was considered in PGM (No 2) v R  NSWCCA 261 at –. A direction in these terms may also be given where the complainant is a child and their evidence was originally given during a pre-recorded evidence hearing in accordance with the procedure in Criminal Procedure Act 1986, Sch 2, Pt 29, Divs 1–4. Note in particular, cl 91 which sets out what a judge must advise a jury in relation to such evidence. See [1-376] for the suggested direction where evidence is given by way of a recording.
Where a witness intermediary is used, see the suggested direction at [1-370].
It must be obvious to you that [the complainant] did not personally give evidence before you. Instead a [video and/or audio recording] of [his/her] evidence from an earlier trial was played to you. This includes the cross-examination of [him/her] by [the accused’s] counsel at that time. The procedure adopted in this trial of playing that recording is usual practice. It is to spare [the complainant] from having to attend court to give that evidence again.
You cannot use the fact that [his/her] evidence was played to you from a [video or audio recording] against the accused. As I said a moment ago, it is usual practice for evidence to be given this way and you should not give the evidence any greater or lesser weight simply because of that. You should also assess the evidence in the same way as you assess the evidence of any other witness.
You cannot speculate about what [the complainant] may have said had [he/she] given evidence in person. You simply act upon the evidence before you and assess it to determine whether you are prepared to act upon it. You may feel there were areas of the evidence that could have been further explored by either party, but you cannot speculate about such a matter or what any further exploration may have revealed, if anything. You must simply consider the evidence that you have.