12 The principles which govern an application for separate trials are tolerably clear:
1) First, there are strong reasons of policy and principle why persons charged with committing an offence jointly or charged as participants in different degrees in relation to the same offence should be tried together ( Webb v The Queen [1994] HCA 30; (1994) 181 CLR 41, 88-9). The concerns which support a joint trial in such circumstances include the trauma and inconvenience to witnesses which are involved in subjecting them to more than one trial; the increased time and expense involved in separate trials; and the highly desirable objective of avoiding inconsistent verdicts as between trials ( R v Jones and Waghorn (1991) 55 A Crim R 159, 185).
2) Secondly, the accused bears the burden of establishing that there is a need for separate trials. Separate trials should not be ordered unless it is demonstrated that there is a real risk of positive injustice as a consequence of a joint trial ( R v Bikic [2000] NSWSC 223; (2000) 112 A Crim R 163, 167 [22]-[23]).
3) Thirdly, while most joint trials may be productive of some degree of prejudice, prejudice of that sort will not be taken to amount to positive injustice unless it is of a kind which is not really amenable to nullification by judicial directions to the jury ( R v Ditroia and Tucci [1981] VR 247, R v Jones and Waghorn (1991) 55 A Crim R 159, 185).
4) Fourthly, one situation in which there may be grounds for separate trials is where the evidence admissible against one accused is significantly different from the evidence admissible against the other ( R v Darby [1982] HCA 32; (1982) 148 CLR 668, 678). Another, is where there is a likelihood that some evidence which is led against one accused will be prejudicial to the other, albeit inadmissible against him or her. A separate trial may be also required in some cases where the evidence against one accused may in effect swamp the jury's consideration of the case against the other accused. The same may be true where the circumstances are such as to create a serious risk of an irrational finding of guilt by association ( R v Chami [2002] NSWCCA 136; (2002) 128 A Crim R 428, 431).
5) In R v Middis (Supreme Court of New South Wales, Hunt J, 27 March 1991, unreported, 4); see also R v Baartma n (Court of Criminal Appeal, 6 October 1994 unreported); R v Piller (1995) 86 A Crim R 249; R v Georgiou [1999] NSWCCA 125, [5]), Hunt CJ at CL identified three categories of case in which an order for separate trials may be warranted as follows:
a) Where the evidence against an applicant is significantly weaker than and different to the evidence admissible against other accused.
b) Where the evidence against a co-accused contains material which is highly prejudicial to the applicant although not admissible against him or her.
c) Where there is a real risk that the weaker Crown case against the applicant will be made immeasurably (in the sense of significantly albeit incomeasurably) stronger by reason of the prejudicial material.
6) It is recognised, however, that such guidelines as have been proffered cannot be exhaustive and that each case will depend upon its own facts. Each case involves a discretionary balancing exercise in which the concerns which support a joint trial must be weighed against the prejudices to the applicant ( R v Alexander [2002] VSCA 183; (2002) 6 VR 53, 67 [31]).