Criminal Forensics--MO vs Signature - How to Tell the Difference Between a Crook's Various Actions

When you watch your favorite CSI TV show, you may have heard of the terms, MO, or modus operandi, and signature that a perpetrator uses when committing a crime. What is an MO and how does it differ from a criminal's signature?

In this article, we will elaborate on the differences between these two terminologies so that when you watch your favorite detective show, you will have a better understanding of what the characters are talking about.

Modus operandi, aka MO, or method of operation, refers to the tools and techniques that a crook uses to commit a crime. This concept is very ancient. In fact, this concept dates back 19th century England when a police constable, Major L.W. Atcherley of the West Riding Yorkshire Constabulary of England, developed a 10-point system for identifying a perpetrator's MO. Scotland Yard later incorporated many of his techniques that are still in use today.

The following factors are considered when identifying a perpetrator's MO:

• Place of the crime


• Point of entry


• Method of entry


• Tools used during the criminal act


• Kinds of objects removed from the scene of a crime


• Time of day when the crime occurred


• The culprit's alibi


• The culprit's accomplices


• Mode of transportation to and from the scene


• Unusual characteristics of the crime, such as killing the house cat or leaving behind a note or object to challenge police

All these factors address the culprit's method of doing things. He finds it necessary to do these things as part of committing the crime.

An MO may evolve over time as the perpetrator finds better ways to commit murder or other kinds of crimes. This may include changing his mode of entry, ploy, disguise, or the time when the attacks occur. He will modify his methods to become more effective and help him avoid being detected.

On the flipside of an MO, a signature refers to an act that has nothing to do with completing the crime or getting away with it. Signatures are important to the perpetrator in a personal way. Torturing the victim, repeatedly stabbing the victim, postmortem mutilation, and the removing of souvenirs or trophies are examples of signatures. These actions are motivated by a killer's fantasies and psychological needs.

Unlike an MO, the perpetrator's signature does not change. His signature may be refined over time, but the basic signature stays the same. For instance, if a serial killer poses his victims in particular manner with a crucifix on the chest, details like candles, bracelets or other ceremonial objects may be included at a later time. The signature has changed, but its basic theme and form stay the same.

The driving force of a signature is the reason for its stability. The perpetrator's signature takes it origin directly from his fantasies. These fantasies develop at a young age and are refined into an obsession from years of mental rehearsal. During the crime, the perpetrator forces the victim to respond in accord with his fantasy. The signature is used only by the culprit to carry out his personal fantasy. Because his fantasy never changes, the signature stays the same.

The next time you watch CSI and hear of the terms MO and signature, you will have a better understanding of their definitions.

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