- 1: a method of procedure; especially : a distinct pattern or method of operation that indicates or suggests the work of a single criminal in more than one crime
Modus operandi (plural modi operandi) is a Latin phrase, approximately translated as "method of operation". The term is used to describe someone's habits or manner of working, their method of operating or functioning. In English, it is often shortened to M.O.
The expression is often used in police work when discussing a crime and addressing the methods employed by the perpetrators. It is also used in criminal profiling, where it can help in finding clues to the offender's psychology. It largely consists of examining the actions used by the individual(s) to execute the crime, prevent its detection and/or facilitate escape.
In the book Criminal Investigation, B.L. Berg explains that a suspect's modus operandi can help in identification, apprehension and/or repression. An M.O. file is an orderly method of recording and coding information designed to reveal habits, traits or practices of criminal suspects. This can then be used to aid in the eventual apprehension of the suspect(s), and can also be used to determine links between crimes.
Also, in the popular television series Criminal Minds, agents at the behavioural analysis unit of the FBI develop profiles of criminals, studying their behavioural traits i.e their M.O in the crime. This helps them to narrow down the suspect pool and apprehend the guilty. Even though profiling in itself is a controversial concept, the use of the person's M.O in the investigation is nothing new.