In times past, a common defense against an accusation of sexual assault was to say, "we did have sex but she consented, and you should believe that she consented because look at her promiscuous sex life." The problem this creates is the likelihood that a jury will disapprove of such a lifestyle, and decide the matter on morals rather than on merits (the facts of the encounter disputed). During the 1970s, legislatures began passing statutes that limited this sort of defense. The statutes broadly prohibit the introduction at trial of evidence of an accuser's sex life or related lifestyle or reputation.
Wisconsin's Rape Shield Statute
In Wisconsin, the rape shield statute is ? 972.11(2), Stats. It is gender neutral and applies to almost any chargeable form of sex abuse. In Wisconsin the primary forms of sex abuse charges are found in ? 940.225 (adult victims) and Ch. 948 (child victims). The rape shield statute prohibits any evidence of or opinion of or reference to sexual conduct that is not part of the encounter disputed. Sexual conduct is broadly defined, and includes not only sexual activities but living arrangements and lifestyle and use of contraceptives.
Exceptions (per Statute)
The statute is worded and enforced to allow only narrow exceptions. The defendant must always ask the judge before trial to allow evidence under one of these exceptions. The main three are that a defendant may introduce evidence of: 1) the accuser's past conduct with the defendant; 2) specific instances of conduct showing the origin of certain physical markers (semen, pregnancy, disease) of who may have had sex with the accuser; and 3) prior untruthful accusations of sex assault by the accuser. Prior untruthful accusations are not limited to those made to police. Manner of dress may be presented to the jury only if its relevance substantially outweighs the danger of unfair influence on the jury.
Exception (per Rules of Evidence)
The defense may also be allowed to introduce evidence that's barred by the rape shield statute if the prosecution "opens the door" to the evidence. If the defense thinks the door has been opened, the defense must first ask the judge to agree. The prosecution may open the door if, on its own initiative, it introduces the prohibited evidence to the jury, in an effort to prove its case. How far the door must be opened depends on the judge. For example, perhaps the accuser exclaims on the witness stand that she would not consent to sex with the defendant because she has this other boyfriend. But the defense has witnesses to say that the accuser has had several boyfriends at once.
Exceptions (per Constitution)
The constitutional right to present a defense sometimes trumps rape shield laws. In Wisconsin, the defense must meet the five-factor Pulizzano test. The defense must show that: 1) the prior act clearly occurred; 2) the act closely resembles the one in the present matter; 3) the prior act is clearly relevant to a material issue in dispute; 4) the evidence is needed by the defense to make its case; and 5) the probative value outweighs the prejudicial effect. Probative value means how important the evidence is to fairly deciding an issue. Prejudicial effect means the danger of unfair influence. The judge decides whether the test is met. As an example, in Pulizzano itself, a woman was accused of molesting a young boy. She wanted to use evidence that the boy obtained his explicit knowledge of the alleged sex acts through this earlier abuse. The high court applied its five-factor test and agreed she should have been allowed to use this evidence.