A co-accused is a person charged alongside another defendant in the same criminal proceedings. Joint trials are the default position in Australian courts: where two or more people are alleged to have participated in the same offence or a connected series of offences, a single trial is considered more efficient, less costly, and less likely to produce inconsistent verdicts. For defendants, that default carries real consequences.
Why courts prefer joint trials
The prosecution's preference for a joint trial is straightforward. Trying co-accused separately means calling the same witnesses twice, tendering the same exhibits twice, and risking two juries reaching contradictory findings on the same facts. Courts share that concern. The Criminal Procedure Act 1986 (NSW) gives courts broad power to join charges and defendants on a single indictment when the charges arise out of the same transaction or series of transactions.
Efficiency alone doesn't override fairness. But the starting point is always joinder. Each co-accused then needs a concrete reason to move the court in a different direction.
How a joint trial actually runs
Each co-accused is entitled to separate legal representation. Their lawyers may take entirely different positions: one might concede part of the prosecution case while another contests it entirely. One might point the finger at the other. This creates a trial within a trial dynamic that juries need careful guidance to manage.
The jury hears evidence against all accused simultaneously. When a confession or out-of-court statement made by one co-accused is tendered, the judge must direct the jury on the limited use they can make of it against the others. That statement is evidence against its maker only. The direction matters because juries naturally want to treat everything they hear as relevant to everyone in the dock.
Cut-throat defences add another layer. If Accused A tells the jury that Accused B was the one who actually carried out the offence, the jury must assess each defendant's case separately. A judge will remind the jury of this regularly throughout the trial, not just at the end.
What a severance application involves
A defendant who believes a joint trial will cause real and substantial prejudice can apply to have the matters separated. This is called a severance application, and courts do not grant them lightly. The applicant must demonstrate that the joint trial creates a genuine, identifiable risk of unfairness, not a merely theoretical one.
Common grounds include situations where one co-accused has made a confession that implicates the others, where the defence of one defendant requires attacking the credibility of a co-accused's evidence, or where the charges against one defendant are so much more serious that their presence on the same indictment risks contaminating how the jury views the others. Courts weigh those concerns against the competing interest in a single, coherent trial.
Tendency and coincidence evidence in joint trials
One of the trickiest evidentiary problems in a joint trial arises when the prosecution wants to use evidence about one co-accused's past conduct to support the case against another. Courts apply the tendency and coincidence evidence provisions of the Evidence Act 1995 (NSW) carefully in this context. The probative value of such evidence must substantially outweigh the danger of unfair prejudice, and judges give juries specific directions on how to reason about it.
A tendency evidence direction in a joint trial context is more complex than in a single-accused trial because the jury must track the permitted reasoning separately for each defendant. Getting that direction wrong can be a ground of appeal.
The verdict and what happens next
A jury in a joint trial returns a separate verdict for each co-accused. It's entirely possible to convict one defendant while acquitting another on the same facts. That outcome doesn't produce a contaminated verdict in itself: different verdicts can reflect genuinely different degrees of participation, different credibility assessments of conflicting testimony, or different defences raised.
Sentencing also runs separately. Each co-accused is sentenced on the findings of fact relevant to their own role, regardless of the sentence received by their co-accused. A person with a minor role in an offence shouldn't receive the same penalty as the principal offender, and sentencing judges are required to differentiate.
Practical implications for defendants
Being tried alongside a co-accused changes the strategic landscape. Your lawyer needs to consider not just the prosecution's case against you, but also what your co-accused's lawyer might do. If your co-accused intends to run a defence that blames you, your legal team needs to know early and respond accordingly.
Instructions to your lawyer should be thorough from the first conference. Tell your lawyer everything you know about your co-accused's likely position. The decisions made before the trial starts, about whether to seek severance, whether to apply to have certain evidence excluded, and how to address the jury on the specific findings required, can be more important than anything that happens during the trial itself.
Ann Valos Criminal Law represents defendants in joint trials across New South Wales. Ann Valos is an accredited criminal law specialist with over 15 years of experience, and the firm's team holds a combined experience of more than 30 years in criminal defence work.