Evidence of someone’s prior acts is generally not admissible in a New York criminal trial. However, under The Guide to New York Evidence Sec. 4.21, evidence of past “crimes, wrongs, or other acts” may be admissible under certain limited situations.
Rule 4.21 specifically prohibits the introduction of prior-act evidence when it is being used to show that the defendant acted in conformity with that act, or if it is being used to show that a person had a propensity to act in a certain way. However, when the evidence is being offered for other reasons, such as to show someone’s motive, intent, opportunity, preparation, the existence of a common plan or scheme, knowledge, identity, or to establish the absence of a mistake, the evidence may be admitted if it is more probative than prejudicial.
Judges are left with the discretion to determine if prior-act evidence should be admitted. In a recent New York domestic violence case, an appellate court discussed Rule 4.21 and its application.