When can the prosecution introduce evidence of the defendant's bad character?

The prosecution can introduce evidence of the defendant's bad character when the defendant "opens the door" to such evidence. This typically occurs when the defendant presents evidence that suggests their good character or when they make statements that imply they are a law-abiding citizen. In these circumstances, the prosecution is then allowed to counteract the impression of the defendant's character.

For instance, if the defendant brings up their reputation for honesty or non-violence, the prosecution may be permitted to introduce evidence of prior bad acts or convictions to challenge that portrayal, thus helping the jury evaluate the defendant's claims authentically. This principle is rooted in the idea of fairness in trial proceedings, where both sides have the opportunity to present relevant information that relates directly to the claims made during the trial.

In contrast, introducing evidence of a defendant's bad character without the defendant first addressing their character would generally be inadmissible as it could lead to unfair prejudice against the defendant. Therefore, the notion of "opening the door" is critical to maintaining the fairness of the trial.