Also known as: collateral evidences · extrinsic evidence
Written by attorneys · grounded in primary & secondary sources — see below
Evidence concerning a matter not closely related to a controlling issue in the case. Such evidence is often excluded when offered as extrinsic proof on impeachment or authentication questions to avoid distracting mini-trials on side issues.
Highland Signal offers an internal investigation file showing that absent declarant Lucy falsified training records. The file is unrelated to the billing fraud at issue. The court excludes the file because it is collateral evidence offered to prove a specific instance of untruthfulness.
A donee offers a letter the donor wrote years earlier describing a non-testamentary motive for a signed document. The letter addresses only the donor's separate business goal and does not illuminate the donative text. The court treats the letter as collateral evidence and declines to consider it when construing the document.
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A contestant offers testimony from the testator's girlfriend that the signed document was executed only to induce her to stay overnight. The testimony concerns a private inducement unrelated to the document's dispositive terms. The court admits the testimony because it shows the document served a collateral non-testamentary purpose.
Clearview Clinic offers a sales representative's oral statement that imaging machines would detect small tumors. The statement conflicts with an "AS IS" clause in the purchase order but does not address any other contract term. The court admits the statement because it is not collateral evidence and forms part of the basis of the bargain.
A beneficiary offers a signed memo in which the testator promised not to revoke a will in exchange for lifetime care. The memo stands apart from the will itself and addresses only the separate agreement. The court admits the memo as the required writing proving the contract terms.
Cassandra offers a video of Caroline stating at a community meeting that the company failed to send maintenance notices. Caroline had not been asked about the statement. The court admits the video after exercising its discretion to dispense with the usual foundation because the statement directly contradicts central testimony.
Rule 608(b) bars extrinsic evidence of specific instances of conduct offered to prove a witness's character for untruthfulness. When a hearsay statement is admitted, Rule 806 places the declarant in the same position as a testifying witness, so the same extrinsic-evidence prohibition applies. The internal investigation file in the Highland Signal case was excluded on this ground because it constituted extrinsic proof of a collateral act of deception.
Supporting sources
Rule 613(b) provides that extrinsic evidence of a prior inconsistent statement may not be admitted until the witness has an opportunity to explain or deny the statement. The rule gives the court discretion to dispense with the foundation when the interests of justice so require. The community-meeting video was admitted under that discretion even though Caroline had not been asked about the statement beforehand.
Supporting sources
Evidence is collateral when its terms are not central or critical to the case against the defendant. In Duffy, testimony about a laundry mark on a shirt was treated as collateral because the charged crime did not turn on possession of the shirt itself and the inscription was simple. The court therefore allowed secondary evidence of the mark without requiring production of the shirt.
Supporting sources
…to depend on the confession' will, in the long run, be less reliable and more subject to abuses than a system which depends on extrinsic evidence independently secured through skillful investigation." Id. , at 488-489 (footnotes omitted). Our interpretation of the Due Process Clause has been shaped by this preference for…