Sometimes what everybody thinks they know is true.

This essay responds to D. Davis and W. C. Follette (2002), who question the value of motive evidence in murder cases. They argue that the evidence that a husband had extramarital affairs, that he heavily insured his wife's life, or that he battered his wife is ordinarily of infinitesimal probative value. We disagree. To be sure, it would be foolish to predict solely on the basis of such evidence that a husband will murder his wife. However, when this kind of evidence is combined with other evidence in a realistic murder case, the evidence can be quite probative. We analyze cases in which it is virtually certain that the victim was murdered but unclear who murdered her, and in which it is uncertain whether the husband murdered the wife or she died by accident. We show that in each case motive evidence, such as a history of battering or of infidelity, can substantially increase the odds of the husband's guilt. We also consider the actual case on which Davis and Follette base their paper. We argue that testimony of Davis on the basis of the analysis presented in their paper was properly excluded, for it would have been misleading and unhelpful.