Modus Operandi

Abstract

Modus operandi (MO) is a Latin term that means method of operating. It refers to the manner in which a crime has been committed. It is comprised of acts and decisions that are necessary to commit a crime, and any related choices made by an offender. Law enforcement has long held to the belief that understanding the methods and techniques criminals use to commit crime is the best way to investigate, identify, and ultimately apprehend them. The modern development and utility of MO as an investigative concept is based largely in classification systems that were originally set forth in Major Lewellyn W. Atcherley handbook Modus Operandi: Criminal Investigation and Detection, first published in 1913. An offender's MO behaviors are learned, and by extension they are dynamic and malleable. This is because MO is affected by time and can change as the offender learns or deteriorates. MO is not consistently comprised of behaviors that are necessarily distinctive or even unique to a particular offender; their crimes will often unfold differently each time, even when committed with the same motive, intent, and methods. MO is best used to help guide investigators to more certain evidence and keep their efforts on course. It should not generally be confused as conclusive evidence suggestive of offender identity when two or more cases are being compared, and certainly not in a legal context.