The characters of witnesses for either the prosecution or the defense are inadmissible, and neither party is permitted to introduce them into a trial. A witness’s credibility, however, is obviously important, and the law permits either side to impeach a witness’s credibility; either side may use reputation evidence or specific examples to do that. This is where a good criminal investigator is invaluable for a defense team; he finds the ammunition you need to go after a witness.
The rules of evidence pertaining to impeachment are separate from those pertaining to character evidence. The rules pertaining to impeachment apply to all witnesses and therefore also apply to the defendant and the victim. If one side attempts to impeach the credibility of a witness, the other side is permitted to “rehabilitate” that credibility with testimony. Rehabilitating a witness does sometimes dispel a negative perception, but very often, jurors will focus on the bad versus the good. If a witness has a credibility issue, the best strategy sometimes is to simply leave that witness off of your witness list unless his or her testimony is absolutely critical.
Character evidence is all about knowledge and preparation. In many situations, your attorney will control whether it becomes an issue at your trial. If character evidence is coming into your trial, your attorney must understand each side’s limitation regarding its introduction. You want the judge or jury focused on what occurred on the date in question. You want them focused on your past only if it will reinforce your attorney’s argument and help create reasonable doubt in the judge or jurors’ minds.