Collateral Facts

"Legal Lexicon":
COLLATERAL FACTS - Facts which are unconnected, or only remotely connected, with the issue or matter in dispute.
As no fair and reasonable inference can be drawn from such facts, they are inadmissible in evidence, for at best they are useless and may be mischievous because they tend to distract the attention of the jury and to mislead them.
It is frequently difficult to ascertain a priori, whether a particular fact offered in evidence, will, or will not clearly appear to be material in the progress of the cause and in such cases it is usual in practice for the court to give credit to the assertion of the counsel who tenders such evidence that the facts will turn out to be material; but this is always within the sound discretion of the court. It is the duty of the counsel, however, to offer evidence, if possible, in such order that each part of it will appear to be pertinent and proper at the time it is offered; and it is expedient to do so as this method tends to the success of a good cause.
When a witness is cross-examined as to collateral facts, the party cross-examining will be bound by the answer and he cannot, in general, contradict him by another witness.
COLLATERAL ISSUE - Where a criminal convict pleads any matter allowed by law in bar of execution; as pregnancy, a pardon, and the like.
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