A person’s motive for committing a crime may tell us a great deal about her and particularly whether we should view her as a “criminal.” But the law says that motive is not intent—and not even mens rea.
Considering the defendant’s motive complicates matters. If Robin Hood intentionally robs the Sheriff (statutory mens rea), the fact that his motive for doing so is to give the proceeds to the poor (arguably a morally good reason, and thus denying “traditional” moral blameworthiness) is irrelevant to his guilt.
Euthanasia raises most directly the difference between the two kinds of mens rea in dealing with motive. A person who (often with the victim’s consent) intentionally disconnects life-prolonging devices or kills with a shotgun at point-blank range for the sole purpose of relieving that person’s suffering certainly has statutory mens rea. However, is he blameworthy? Does he have traditional mens rea? Motive suggests he does not have traditional mens rea. Yet most courts today would exclude evidence of such a motive.
Motive is admissible, however, to bolster the prosecutor’s case, since from motive the jury may well infer mens rea. For example, Gertrude, who has just run over Jillian with her car, claims she did not see Jillian. So far as we initially know, they are total strangers. Charged with purposely killing Jillian, Gertrude is likely to be acquitted. We simply can’t see why Gertrude would purposely kill the victim, even if the external evidence suggests that (1) it was a bright and sunny day; (2) Gertrude traveled over 500 feet before she hit Jillian, who was on the sidewalk; (3) Gertrude never hit the brakes. However, if we discover that Jillian is having an affair with Gertrude’s husband, or that Gertrude stood to inherit from Jillian, or that Jillian was blocking Gertrude’s advancement in her field, we might now be willing to infer that Gertrude purposely killed Jillian, because she had a motive for doing so. It is the lack of apparent motive that spurs Hitchcock’s great film, Strangers on a Train, where strangers agree to “swap murders” in the belief that the police will not suspect them of “motiveless” crimes.
If motive is not relevant to the determination of guilt, the judge may—or may not—consider it at the time of sentencing. Even if Robin Hood and Smokey the Rat are both robbers, we may tend to think Robin deserves less punishment. Similarly, bad motive may seem to warrant increased punishment. Assault alone may be a crime. If it is motivated by racial animosity, we may consider it worthy of more punishment.