The underlying purpose of the “rule of completeness” – an evidentiary rule that governs the admissibility of certain statements or recordings – is fairness. A party should not be able to mislead the finder of fact with evidence that is incomplete or taken out of context.
The example cited by McCormick on Evidence § 56 is the expression – “The fool hath said in his heart, there is no God” – where only the latter phrase is quoted. Writes McCormick: “You could quote the Bible as saying ‘there is no God’; but to do so would be a misleading half-truth because it divorces the quotation from its context.”
To guard against the inherent unfairness of introducing such misleading evidence, the opposing party should thus have the ability not only to cross-examine the witness about the incomplete evidence but also to introduce – either directly or through the proponent – the accompanying evidence needed to put the statement into context. This could include evidence that might be otherwise inadmissible; as, for example, with respect to hearsay.
Moreover, because of the lasting and potentially unconscious impact of the partial evidence on the finder of fact, in some cases the evidence should be precluded from being introduced at all.
The rule is codified in Federal Rule of Evidence 106: “When a writing or recorded statement or part thereof is introduced by a party, an adverse party may require the introduction at that time of any other part or any other writing or recorded statement which ought in fairness to be considered contemporaneously with it.”
The common law rule with respect to the rule of completeness has been adopted in D.C. through case law. For example, the D.C. Court of Appeals held in Diggs v. United States, 28 A.3d 585, 597 (D.C. 2011) that “the rule contemplates that other parts of the statement should be admitted, in the trial court’s discretion, when this is necessary to explain the admitted portion, to place it into context, or to avoid misleading the trier of fact.”
The Court continues: “As applied in a criminal case, the rule is ‘typically implicated when the prosecution selectively introduces only the inculpatory portions of a defendant’s statement, and fairness requires that exculpatory parts of the same statement be considered as well so that the defendant’s meaning is not distorted or misunderstood.” Id. (quoting Henderson v. United States, 632 A.2d 419, 426 (D.C. 1993).