Hearsay - Co-conspirator's Exception. R v Kler
In R v Kler (Ont CA, 2017) the Court of Appeal comments usefully on the evidentiary issues of the co-conspirator's exception to the hearsay rule:
The Co-conspirators' Exception
 The co-conspirators' exception to the hearsay rule permits statements made by a person engaged in an unlawful conspiracy to be received as admissions against all those acting in concert if the declarations were made while the conspiracy was ongoing and were made towards the accomplishment of the common object: Mapara, at para. 8.
 From the statement of the rule, we learn several things.
 First, not every statement made by a fellow conspirator can be enlisted in proof of another conspirator's membership in the conspiracy: R. v. Yumnu, 2010 ONCA 637 (CanLII), 260 C.C.C. (3d) 421, affirmed, 2012 SCC 73 (CanLII),  3 S.C.R. 777, at para. 341. The statement must be made by a "person engaged in an unlawful conspiracy". And as we shall see, for these purposes, a person is "engaged in an unlawful conspiracy" if his or her own acts or statements establish his or her probable membership in it.
 Second, a matter of timing, or better said "contemporaneity". The statement must be made by the conspirator "while the conspiracy was ongoing": Mapara, at para. 8; Carter, at p. 947. That said, on some occasions, statements made after the offence object of the conspiracy has been committed may be admissible under this exception: Yumnu, at para. 341; R. v. Sauvé (2004), 2004 CanLII 9054 (ON CA), 182 C.C.C. (3d) 321 (Ont. C.A.), leave to appeal refused,  1 S.C.R. xv, at paras. 115-18.
 Third, the statement of the co-conspirator must be made "in furtherance of" the offence object of the conspiracy, that is to say, for the purpose of achieving its goal: R. v. Puddicombe, 2013 ONCA 506 (CanLII), 299 C.C.C. (3d) 503, leave to appeal refused,  S.C.C.A. No. 496, at para. 116. Provided there is evidence capable of sustaining a finding that a statement of a co-conspirator was "in furtherance" of the common offence object, the ultimate decision about whether the statement is "in furtherance" is for the jury: Puddicombe, at para. 116. See also R. v. Mota (1979), 46 C.C.C. (2d) 273 (Ont. C.A.), at pp. 282-83.
 A final point concerns the scope of the co-conspirators' exception. Here, we are concerned with a specific statement, but the exception extends beyond statements to acts done by co-conspirators during the currency of the conspiracy in furtherance of its objects: see e.g. R. v. Garofoli (1988), 1988 CanLII 3270 (ON CA), 41 C.C.C. (3d) 97 (Ont. C.A.), at pp. 135-36, reversed on other grounds, 1990 CanLII 52 (SCC),  2 S.C.R. 1421; R. v. Baron (1976), 1976 CanLII 775 (ON CA), 31 C.C.C. (2d) 525 (Ont. C.A.), at p. 533.
The Co-conspirators' Exception and the Principled Approach
 Despite the ascendency of the principled approach to the admissibility of hearsay, the traditional or category exceptions remain presumptively in place, including the co-conspirators' exception to the hearsay rule: Mapara, at para. 15.
 A hearsay exception, such as the co-conspirators' exception, can be challenged to determine whether it is supported by the indicia of necessity and reliability, required by the principled approach. If necessary, the traditional exception may be modified to bring it in line with the principled approach: Mapara, at para. 15.
 In Mapara, the co-conspirators' exception to the hearsay rule was challenged as failing to accord with the fundamental criteria that underlie the exceptions to the hearsay rule and are the twin requirements of the principled approach – necessity and reliability. The Court concluded that the co-conspirators' exception met the necessity and reliability requirements of the principled approach. The continued vitality of the co-conspirators' exception was affirmed: Mapara, at para. 31.
 The Mapara court found the indicium of necessity established because of the combined effect of:
i. the non-compellability of a co-accused declarant, Wasfi, who's case was severed from that of Mapara at the end of the case for the Crown;See Mapara, at para. 18; R. v. Chang (2003), 2003 CanLII 29135 (ON CA), 173 C.C.C. (3d) 397 (Ont. C.A.), at para. 105.
ii. the undesirability of separate trials for alleged co-conspirators; and
iii. the evidentiary value of contemporaneous declarations made in furtherance of an alleged conspiracy.
 The Court in Mapara found the reliability requirement met because the conditions imposed by Carter on the use of evidence admitted under the co-conspirators' exception provided sufficient circumstantial guarantees of trustworthiness necessary to permit the evidence to be received:
i. proof of the conspiracy alleged beyond a reasonable doubt;See Mapara, at paras. 22-26.
ii. probable participation in the conspiracy by the accused based on his or her own words and conduct; and
iii. the requirement that the acts and declarations of other likely conspirators be in furtherance of the conspiracy to be available in proof of an individual member's guilt.