Generally, the term modus
operandi (M.O.) represents the functional components which are necessary for
an offender to be successful in committing a crime (Keppel, 1997; Douglas et
al. 1992). Historically, M.O. has been used to link cases because
offenders will use similar methods during the commission of their crimes.
M.O. can include factors such as; a time of day or location an offender
chooses to strike, the type of victim, points or techniques for gaining
entry, as well as tools used for committing the crime.
However, M.O. can change over time as offenders become more experienced or
learn new techniques that will make them more successful or lower their
chances of being identified. For example, an offender may always
strike at night, gaining entry to the location by using a glasscutter and
shooting a victim. This can completely change however, if the offender
learns that using a suction cup with the glasscutter and a knife to kill the
victim will create less noise. Again, everything mentioned above are
factors that are necessary to commit the crime.
Signature aspects on the other hand, are behaviors that go beyond what is
necessary to commit the crime and fulfill a psychological need of the
offender. Unlike M.O., signature aspects are stable over time and will
be witnessed at each crime scene throughout a series. Although there
may be subtle differences from crime to crime, there will be an evident
theme. As this theme represents a psychological need of the offender,
signature seems to be based heavily upon, and reflect the offender's
Signature aspects are symbolic and hold special significance to the
offender, and may not be understood by anyone other than the offender.
If over a series of murders the victim's arms are left crossed upon their
chests, this is significant to the offender and goes beyond what is
necessary to commit the crime. The actual reason or meaning may not be
understood by investigators, but there is a clear indication that each of
these crimes were committed by the same offender for whom the crossing of
the arms does have significance.
Hazelwood and Warren (2004) have also
incorporated a description of ritual into the discussion of M.O. and
signature to indicate the fantasy and motivational factors that are at times
an aspect of violent crimes. Ritual is indicated at crime scenes as
behaviors that are psychologically based and fulfill a need of the offender,
which is also not necessary for the successful commission of a crime.
Ritual may be indicated at a crime scene with bindings on the victim, posing
of victims, unique markings on victims, or any other behaviors that are
symbolic and fulfill a psychological need of the offender. Ritual and
signature seem to interact and produce behaviors that demonstrate the basic
needs of the offender and can provide investigators with an indication of
the offender's motivation and fantasy.
M.O., ritual and signature are all important
concepts to consider when investigating a series of crimes. By
analyzing behaviors at crime scenes investigators are able to perform
linkage analysis and determine if they are looking for one or more
I would like to begin a section here to list signature aspects that our
visitors have some across while reading about or researching the topic.
If you have others to add to this list, please e-mail me and I will post
An offender forced a victim to call her husband and ask that he come home
for some reason. When the husband arrived, he was tied to a chair and
forced to watch as the offender raped his wife. (Douglas et al., 1992)
Douglas, J.E., Burgess, A.W., Burgess, A.G., & Ressler, R.K. (1992).
Crime classification manual: A standard system for investigating and
classifying violent crimes. San Francisco, CA: Jossey-Bass.
Keppel, R.D., & Birnes, W.J. (1997). Signature killers: Interpreting the
calling cards of the serial murderer. New York, NY: Pocket Books.