If the prosecution has their hands on some choice evidence that can be used as a "gotcha" against the defense and catch them off guard, are they allowed to do that? Or are the prosecution expected to share such evidence with the defense (perhaps upon request) beforehand, allowing the defense to prepare for it? Basically, are the prosecution/defense supposed to know/anticipate the main evidence/witnesses of each party? Or are they allowed to keep some things secret and "surprise" the other side during the trial as an attempt to gain an advantage? And what things are they allowed to (or not allowed to keep) hidden away like that?

As an example, perhaps the defendant has some video evidence of him away from the crime scene. Is the defence allowed to bring up that evidence out of nowhere during the trial and blindside the prosecution? Or does the prosecution have right to know of such evidence beforehand so they can prepare a rebuttle with regards to it?


2 Answers 2


Unsurprisingly, there is a rule of criminal procedure at the federal level, rule 16. It is complicated, but here are the broad strokes of that requirement. There are a number of requirements of government disclosure (a), and then there are defendant's disclosure rules (b). If defendant requests, the government must disclose defendants statements, also the defendant's prior record, documents and objects, test results. There is also a duty to disclose w.r.t. expert witnesses. Specifically excluded are government-internal documents regarding the investigation or prosecution (things that won't be introduced at trial), and grand jury transcripts. There are conditions and exceptions within the exceptions: all of these obligations are "if the defendant requests".

The defendant must disclose certain documents if the defendant requests and the government complies under Rule 16(a)(1)(E) which is the government's obligation to disclose objects. Then

the defendant must permit the government, upon request, to inspect and to copy or photograph books, papers, documents, data, photographs, tangible objects, buildings or places, or copies or portions of any of these items

if the defendant has it and intends to use it. There is a similar requirement to report test results in his possession that he intends to use, if he has so requested of the government, and also expert witnesses have to be disclosed. Not subject to disclosure by the defense are anything statement-like made by or to the defendant or his attorney by defendant, a witness or a prospective witness (on either side). This is pre-trial discovery. Rule 26.2 applies during trial:

After a witness other than the defendant has testified on direct examination, the court, on motion of a party who did not call the witness, must order an attorney for the government or the defendant and the defendant's attorney to produce, for the examination and use of the moving party, any statement of the witness that is in their possession and that relates to the subject matter of the witness's testimony.

So the government or defense must comply with that order as well.

"Surprise witnesses" are allowed. The party discovering such a witness must be genuinely "surprised", so a party can't deliberately suppress information that they have a eyewitness and a photograph, but if they discover such evidence late in the game, it can be admissible.

  • To oversimplify, the prosecution must disclose all of its evidence with only narrow exceptions, and the defense must disclose very little and primarily only in cases where a reasonable opportunity to react to something would cause a great delay and might change the tenor and focus of the entire case (e.g. an intent to make an alibi or insanity defense).
    – ohwilleke
    Feb 21, 2023 at 22:02

The Crown (prosecution) must disclose all material relating to the accused's case. This obligation is near absolute. The Crown must disclose all information unless it is "clearly irrelevant, privileged, or its disclosure is otherwise governed by law." See R. v. McNeil, 2009 SCC 3.

The accused/defendant has generally has no reciprocal obligation. See R. v. Brown, 2002 SCC 32, citing R. v. Stinchcombe, [1991] 3 S.C.R. 326.

But there are some narrow exceptions or practical realities: notice of a Charter challenge, notice of an alibi defence, notice of an expert witness in order to avoid unnecessary adjournment, providing fair opportunity during cross-examination of Crown witnesses for them to respond to what will later be contradictory evidence in the defence's case, etc.

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