Canadian Criminal Procedure and Practice/Trials/Trial Process
Purpose of a trial 
A trial is the process by which a judge attempts to ascertain the truth in order to convict the guilty and acquit the innocent. The process does not go so far as to determine "actual innocence" as the standard of proof a trial is proof beyond reasonable doubt and does not evaluate degrees of acquittal and is not the ultimate purpose of criminal law.
The trial fundamentally is "about the search for the truth as well as fairness to the accused". This is guided by these principles:
- the presumption of innocence
- the right against self-incrimination 
- the ultimate burden on the crown to prove guilt beyond a reasonable doubt.
- R. v. Levogiannis,  4 S.C.R. 475 ("The goal of the court process is truth seeking and, to that end, the evidence of all those involved in judicial proceedings must be given in a way that is most favourable to eliciting the truth.")
R. v. Nikolovski,  3 SCR 1197, ("The ultimate aim of any trial, criminal or civil, must be to seek and to ascertain the truth.")
R. v. G. (B.), 1999 CanLII 690 (SCC),  2 SCR 475 ("[T]he essential principle of every criminal trial [is] the search for truth.")
- R. v. Mullins-Johnson, 2007 ONCA 720
- R v Handy, 2002 SCC 56 ("[t]he criminal trial is, after all, about the search for truth as well fairness to an accused")
- R v Handy  2 S.C.R. 908, 2002 SCC 56 at 44
- s. 11(d) of the Charter
- Section 11(c) of the Charter
Crown's Case 
The Crown will always be the first party to call evidence. It is expected that the crown will call all available witnesses that can provide evidence to establish the elements of the offences charged beyond a reasonable doubt.
The Crown is expected to call, as part of its case, evidence that may rebut any alibi evidence and evidence of similar facts.
- R v Biddle  1 SCR 761
Defence's Case 
At the end of the Crown's case the Defence will be permitted to either make a motion for directed verdict, elect to call evidence, or elect not to call evidence.
If the accused elects to call evidence, an opening statement may be given to introduce the trier-of-fact to the defence's case.
The defence has discretion on the order of the calling of witnesses.
If the accused does not call evidence, there will be no need for a opening statement. The case will proceed to closing statements beginning with the Crown's submissions.
Reply or Rebuttal 
On closing of the crown's case, the crown is expected to have presented all relevant evidence available. The judge should not allow Crown to "split" it's case and present any part of its case after the defence.
The judge may permit the crown to present further evidence at the close of the defence's case.
The evidence is limited only to matters that were raised in the defence evidence.
If the Crown evidence could have been reasonably anticipated as being relevant during the Crown's case then it should have been called then and should not be permitted to be called in rebuttal.
- R. v. Melnichuk, 1997 CanLII 383 (SCC),  1 SCR 602
- R v Kuyan (1988) 43 CCC (#d) 339
- R v Perry (1977), 36 C.C.C. (2d) 209 (Ont. C.A.)
Re-Opening the Case 
Once a party has closed their case, it is presumed they have finished presenting their evidence. It is the judge's discretion to allow a party, usually the crown, to re-open their case.
The factors to consider in exercising discretion to re-open a case prior to verdict are:
- whether the evidence is relevant to a material issue in the case;
- the potential prejudice to the other party, if reopening is permitted; and
- the effect of permitting reopening on the orderly and expeditious conduct of the trial.
The main consideration is the potential prejudice to the opposing side by re-opening the case.
The test to re-open the defence's case is more stringent post-conviction in order "to protect the integrity of the process, including the enhanced interest in finality". In such cases the test will be the same for admitting fresh evidence on appeal.
- R v Hayward (1993) 86 CCC (3d) 193 at para. 17-19
- R v Hayward, (1993) 86 CCC (3d) 193 (ONCA)
- R. v. Kowall 1996 CanLII 411 (ON CA), (1996), 92 O.A.C. 82, 108 C.C.C. (3d) 481 at para. 31
- See R. v. Palmer, 1979 CanLII 8 (SCC),  1 S.C.R. 759, cited by Kowall at para. 31
Re-opening the Crown's Case 
The judge may consider an application by the Crown to reopen their case. The standard will depend on what stage in the trial the application is made.
The judge has discretion to reopen the case "to correct some oversight or to prove a matter which it had failed to do inadvertently, provided that there was no prejudice to the accused." However, "[o]nce the defence had begun to present its case, the judge’s discretion [is] narrowly restricted" and may only be reopened "to prove a matter, ex improviso, which no human ingenuity could have foreseen." 
- Robillard v. The Queen, 1978 CanLII 200 (SCC),  2 S.C.R. 728
R. v. P. (M.B.), 1994 CanLII 125 (SCC),  1 S.C.R. 555
R. v. G. (S.G.), 1997 CanLII 311 (SCC),  2 S.C.R. 716
See also R. E. Salhany, Q.C., Canadian Criminal Procedure, 6th ed., looseleaf (Aurora: Thomson Reuters Canada Limited, 2010) vol. 1 at paras. 6.3975, 6.3980, 6.3990