[Latin, Method of working.] A term used by law enforcement authorities to describe the particular manner in which a crime is committed.
The term modus operandi is most commonly used in criminal cases. It is sometimes referred to by its initials, M.O. The prosecution in a criminal case does not have to prove modus operandi in any crime. However, identifying and proving the modus operandi of a crime can help the prosecution prove that it was the defendant who committed the crime charged.
Modus operandi evidence is helpful to the prosecution if the prosecution has evidence of crimes committed by the defendant that are similar to the crime charged. The crimes need not be identical, but the prosecution must make a strong and persuasive showing of similarity between the crime charged and the other crimes. The prosecution may introduce evidence from prior or subsequent crimes to prove modus operandi only if the other crimes share peculiar and distinctive features with the crime charged. The features must be uncommon and rarely seen in other crimes, and they must be so distinct that they can be recognized as the handiwork of the same person.
For example, assume that a defendant is on trial for armed ROBBERY. In the robbery the defendant is alleged to have brandished a pistol and ordered the victim to relinquish cash and valuables. Assume further that the defendant has committed armed robbery in the past by brandishing a pistol and demanding cash and valuables. A prosecutor might be able to introduce the evidence into trial to show the defendant's motive, intent, or state of mind, or to identify the weapon used in the crime. However, the prosecutor could not argue to the judge or jury that the robberies were so similar as to demonstrate that it was the defendant who committed that particular robbery, because it is not unusual for a robber to brandish a pistol and demand cash and valuables in the course of an armed robbery.
Now assume that a defendant is charged with robbing a movie theater that was showing the movie Showgirls and that the defendant was wearing a glittering, flamboyant Las Vegas-style cabaret costume during the robbery. Assume
further that the prosecution has evidence that the defendant, while dressed as a Las Vegas dancer, has robbed other movie theaters showing the movie Showgirls. The prosecution could introduce this evidence into trial to prove modus operandi and show that it was the defendant who committed the crime, because the method of armed robbery used in the crimes was both similar and distinctive.
When offering evidence to prove modus operandi, the prosecution does not have to prove BEYOND A REASONABLE DOUBT that the other crimes occurred. Rather, the prosecution simply must present sufficient evidence to show that the act took place and was committed by the defendant.