Modus operandi of serial killers

The modus operandi is a functional behaviour that pursues three objectives: to protect the identity of the aggressor, to ensure the success of the aggression and to facilitate escape


The modus operandi refers to the "how of the crime", therefore, it will be different from the "why", which would refer to the real motivation or signature of the crime. It is very necessary to differentiate between these aspects because they tend to be generalised or used interchangeably nowadays.  

Mildren M. Gross defined modus operandi as the manner in which a crime has been committed. We can therefore understand it as the actions and behaviours that are aimed at committing or facilitating the commission of the crime.  

The modus operandi will be based on the acts that are strictly necessary to carry out the commission of the crime, thus we can identify the modus operandi as the actions carried out by the perpetrator during the commission of a crime.  

The modus operandi is dynamic, it evolves, that is why we cannot focus only on the modus operandi of a crime, but study them all together, because normally the modus operandi tends to evolve as the offender's experience increases, as he gradually becomes more specialised.  


The modus operandi is a functional behaviour that is responsible for or pursues the achievement of three objectives: 

  1. Protect the identity of the offender. 
  2. To ensure the success of the aggression. 
  3. To facilitate escape. 

The modus operandi provides us with a lot of information, including the supposed intelligence of the perpetrator, because by analysing the way in which the acts are carried out, we can see a supposed relationship of familiarity with a certain technique. 

There are certain factors that can help to make the modus operandi more and more perfect and, therefore, the risk lower, as we will explain below. In terms of the ways or situations by which the modus operandi is specialised and improved are as follows: 

  • More sophisticated and better tools. 
  • Criminological culture. 
  • Professional expertise. 
  • Increased caution due to police pressure.  

While it is true that as the perpetrator commits more crimes, he will gain more experience and, therefore, the modus operandi will increase, the opposite can happen, and the modus operandi will involute. 

Juan Enrique Soto (CNP) established the indices of deterioration of the modus operandi, which are summarised as follows:  

  • Overconfidence. 
  • Impairment of cognitive, motor or perceptual skills. 
  • Drug and alcohol use. 
  • Personal impairment. 
  • Pressure from the police. 

With any one of these factors, although most of the time several of them are linked, the subject will make more mistakes and will therefore be more vulnerable to identification and arrest. For this reason, it will be necessary to look at all the modus operandi, and more specifically the one carried out in the commission of the first crime by the criminal, as this is where it is most likely that he will commit the greatest number of errors, although the profiler will have to determine whether we are dealing with an initial or an evolved modus operandi.  


We have mentioned that the modus operandi has the primary objective of committing the crime, as well as making it as difficult as possible for the perpetrator, i.e. to protect him, however, when analysing the modus operandi according to the achievement of objectives, we find two levels:  

  • Low-risk modus operandi: Modus operandi that evidences great planning, great skill and optimal acts of precaution, during and after the criminal act. The time, place and victim are selected with great skill to further his interests.  
  • High-risk modus operandi: In this case we are faced with a modus operandi characterised by improvisation, little preparation, where acts of precaution are conspicuous by their absence, and there is no predetermined victim or a specific point, therefore, the possibility of the act being carried out, i.e. consummated, is lower with respect to the modus operandi described above.  

In line with what has been said above regarding the refinement of the modus operandi, it should be stressed that Darwin's theory comes into play here.  This would explain that due to the evolutionary development of the species, criminals who improve and become more prepared, i.e. have a more specialised modus operandi, will have a lower risk of being caught.  

For the evolution of the modus operandi it is not necessary to wait too long, depending on the crime it may vary from one single criminal act to the next, so we will have to be very careful when linking a crime only to the behaviours described in the modus operandi. 

Also of special relevance are the acts of precaution, understood as "actions carried out by the aggressor, before, during and after the crime, to hide, confuse and mislead investigators as to how the events took place and mainly aimed at preventing their identification.  

In this sense, we can see that a detailed study of the modus operandi used is fundamental when it comes to studying and understanding a series of crimes, as it is from this that the investigation can be carried out, being an optimal starting point for the investigation.  

Jairo Sánchez Gómez, coordinator of the Criminology area at Sec2Crime 


GROSS, H. (1924), Criminal Investigation. Traducción de System Ker Kriminalistik. Nueva York: Sweet & Maxwell. 

DOUGLAS, J., & OLSHAKER, M. (1995). Mind Hunter: Inside The FBI’s Elite Serial Crime Unit. New York, NY: Simon & Schuster. 

JIMÉNEZ. J. (2010) Manual práctico del perfil criminológico. Valladolid: Lex nova. 

Go to note 3 

RESSLER, R.K.- SHACHTMAN, T. (1995), El que lucha con monstruos. Barcelona: Seix Barral.