Modus Operandi Law and Legal Definition
Modus operandi is a characteristic pattern of methods of a repeated criminal act, used to identify the culprit. It is often referred to as "M.O." The modus operandi of a particular has often been held to have been a proper subject for expert testimony, under the general principles that expert testimony is admissible if the subject matter meets the ordinary test of relevance and is sufficiently beyond ordinary experience as to render the testimony of probable assistance to the jury, and that the admission of expert testimony is a matter resting within the broad discretion of the trial judge and is not to be disturbed unless clearly erroneous.
For example, in pickpocket prosecutions modus operandi testimony has been held properly admitted to enable the jury to connect a defendant's apparently noncriminal act of bumping the victim to create a distraction enabling a partner to remove a wallet without being detected.