Criminal Investigative Analysis in Sex-Related Homicide


The Application of Modus Operandi and Signature



By Vernon J. Geberth, M.S., M.P.S. 
Homicide and Forensic Consultant

©2015 Vernon J. Geberth, Practical Homicide Investigation
Originally published by Law & Order Magazine, Vol. 63 No. 6 June, 2015 pp 28-30

Under the title, "Criminal Investigative ANALYSIS IN SEX-RELATED HOMICIDE
This PHI version of the Article has been expanded for Research and Clarity.


As a homicide investigator you should focus on the similarities of cases as you develop an investigative

hypothesis. If you have a second victim killed in a similar fashion with an M.O. and Signature that is

consistent with the other case than you must think of the possibility of a serial killer.




Criminal investigative analysis, heretofore known as criminal profiling, is a systematic methodology using clues left at a crime scene to gain insight about the crime and the offender.

It is a process of combining knowledge of behavioral sciences with the facts of the investigation.


Homicide detectives follow logical steps during the investigation. They examine the crime scene. They gather evidence and information from various sources. They attempt to reconstruct the incident using the components of the crime including forensic evidence and any physical and/or psychological attributes of the offender to develop a theory about the incident.  [1]


Investigators then assess this data to see whether or not their theory is consistent with the facts of the case and whether or not they can determine and interpret any significant criminal behavior that will assist them in ascertaining the identity of the offender. The investigators brainstorm the case during the investigative critique. They use their intuition, follow hunches, and make educated guesses based upon their extensive personal experience in homicide investigation.  In fact, an effective homicide detective is usually someone who has taken his experience and has enhanced it with knowledge, flexibility, and common sense.


The process starts with some basic investigative questions as one examines the facts and circumstances of the case. What took place? “Why did it occur? And “Who could have done it”

The investigator then attempts to ascertain the “Modus Operandi” utilized in the offense and the “Signature” of the offender.


An effective Criminal Investigative Analysis is synopsized as follows:

The Criminal Investigative Analysis

u     Analyzes the Initial Crime Scene Investigation.

v     Evaluates the Victimology.

w     Evaluates the Physical and Trace evidence.

x     Reviews Wound Patterns.

y     Evaluates the Toxicological Examination Results. 

z     Evaluates the Geographical Profile Information.

         (including demographics and crime patterns)

{     Analyzes the Witness accounts.

|     Performs a Personality Assessment of any Potential Suspects.


Determining Motivation


An extremely important aspect of homicide investigation is the determination of the motive for the killing. In the sex-related homicide, there are a number of possibilities to consider. Sex-related homicides include rape–murders, serial murders, killings involving anal and oral sodomy and other acts of sexual perversion, and interpersonal violence scenarios.


No one acts without motivation.  The motivations may sometimes be revealed in the presentation of the body in the crime. The investigative challenge is to discover this perverse or seemingly irrational logic and then apply this information to the case.


A careful search should always be conducted at the crime scene and within the surrounding area for evidence of sexual activity. This includes the presence of sexual assault activity as well as substitute and paraphilic behaviors. This evidence may be seminal fluid in the vagina, mouth, nasal area, or rectum. Semen and other evidence may be discovered outside the body or upon the clothing. Pornographic books, videos, magazines, and/or photographs may be found at the crime scene. The photographs may depict the victim involved in sexual activity. Writings or messages may be left by the offender at the crime scene and/or upon the body of the deceased. In any event, these factors are important in determining the type of sexual activity that may have taken place.


Human behavior, although unpredictable, is often repetitive. Research has indicated that certain actions engaged in at the homicide crime scene by certain types of personalities will be repeated in other homicide investigations. The homicide detective who has enhanced his experience with a comprehension of the psychodynamics of human behavior will be able to develop a base of knowledge that can be applied to the review of similar cases.[2]


The reason and motivation for the crime are an extremely important consideration in establishing the investigative direction. Was the murder the result of a lover’s quarrel?


Is the case attributed to interpersonal violence? Does it appear the victim was killed during a rape or sodomy attempt? Is the killing sexually oriented? Is there a psychotic motive, which sometimes appears to be motiveless or bizarre? Is the homicide the work of a sexual psychopath, with sadistic or impulsive implications? Was the body sexually posed? What does this suggest? Each of these scenarios suggests a specific course of action.


However, in sex-related homicide investigations, the motivation behind the killing may not be immediately ascertained. Even when you do believe that you have determined the motive, my experience suggests exercising caution.


Determining Motivation in Cases Involving Sexual Posing

Crime scene staging and sexual posing and/or positioning of a body in a crime scene are recognized homicide investigation phenomena and may provide the reason for such the murder. presentation. Was the staging done to satisfy some psychological need? Was the staging a result of anger or retaliation? Was the staging done to evade detection?

How frequent these motivations are seen in staged or other homicides, or how often staging actually occurs, are not typically recorded in justice system data. The author conducted a survey on this phenomenon in a journal article entitled; Crime Scene Staging: An Exploratory Study of The Frequency and Characteristics of Sexual Posing in Homicides[3]


The author had access to 185 cases of sexual posing in his dataset of 44,541 homicides. These 185 cases represented slightly less than 1% of all of the homicides. Examination of these cases revealed the offender’s motivation could be sorted into Three Categories.


Fantasy Driven Behavior

This was the most common motivation. The posing was done to satisfy a perverse sexual fantasy.  Sexual Sadists rely heavily on Fantasy and Ritual to obtain sexual satisfaction.  The sexual manipulation of the victim’s body including Posing, propping, sexual mutilation, defeminization and evisceration are examples of fantasy driven behavior. 



This is the second most common motivation in sexual manipulation of the body. The offender used sex as a weapon to punish and degrade the woman.  The posing of the body was done to further degrade the victim out of anger or revenge. 


Staging The Scene

This was the third motivation for sexual posing of the body. The offender consciously attempted to mislead and thwart the police investigation by making the murder appear to be sexual when in reality the murder was based on interpersonal violence.



The Identification of the Victim

The identification of the victim is a crucial consideration in determining motivation. An intensive investigation into the victim’s background, lifestyle, and associations many times will reveal a possible motive. An examination of any relationships, acquaintances, and risk factors may provide a clue to the “Who could have done it?” scenario. For example, “With whom does the victim live?” Who was with the victim last?”Does it appear that the victim knew his or her assailant?” “What is the victim’s current social status?” “Why was this particular victim selected”?  “Does the crime appear to be a “stranger-homicide? “Was the deceased in a high-risk occupation (call girl or prostitute)?”  Was the victim a runaway or?” “Was the victim a late-hours worker, e.g., waitress or service worker, who had to travel alone at night?” “What method of transportation did the victim utilize”? “What route did the victim travel?” “Were there any recent sexual incidents in the area, such as voyeurism (Peeping Tom cases) or fetish burglaries? Are there any rape or sexual assault patterns?”


One of the most significant factors to consider in death investigation is victimology. In sex-related events, victimology becomes paramount in the assessment and analysis of “Who was the victim and what was going on in his or her life at the time of the event?”[4]



The Crime Scene Assessment

At every crime scene the offender inadvertently leaves messages or clues as to his or her identity, indicating the motivation and/or drive for the crime.  Crime scene assessment focuses on the connection   among the major elements in a homicide investigation. Examples of the major elements would be the location, the victim, the offender, crime scene forensics and autopsy protocols.


The location where an offense took place and the body disposal site can provide insight into the nature and background of an offender.  Research indicates that the distance between the murder site and the disposal site is usually short.


Significant scenes and routes to the scene to consider

         Last seen alive

         Initial contact scene

         Attack scene

         Murder site

         Body disposal site



A victim whose body was sexually mutilated dumped at an outdoor location with all identification removed is highly suggestive of an organized offender who engaged in these activities at one location and had access to a vehicle in order to separate the event from his comfort zone.  While a victim sexually assaulted and posed in her residence might suggest an offender who resides in the area and may have had some previous interaction with the victim. The evaluation of the wound structures of a nude or semi-nude male victim who was found multiply stabbed in the back and neck might suggest a sex crime where the offender who was homosexually oriented.


Significant Components to consider

         Location of offense

         Method of entry

         Protection of identity

         Weapons used

         Evidence of Ritualistic Behavior


Crime scene forensics goes beyond the recovery of physical evidence.  The other consideration is the significance of what the offender did in the scene, what was done to the victim.


Significant Components to consider

         Physical Materials

         Victim incapacitation

         Sexual evidence

         Offender Forensically aware?

         Was the offender injured?

         Are there any missing items?

         Blood distribution

         Linking evidence



Modus Operandi and Signature


In addition to victimology and presentation of the victim in the crime scene the investigator must understand the significance of M.O. and Signature especially in sex-related incidents.

Modus Operandi is a learned behavior that tends to change as offenders gain experience and/or build confidence in their crimes.  Some reasons for a change in an offender M.O. could be attributed to experience, maturity, education, incarceration/jail time, criminal versatility, and/or technology.


Some examples of modus operandi are an offender who brings a weapon, uses a con, the times of crime, The days of the week, intelligence gathering (Stalking), methods of control of victim, use of the victim’s vehicle, and the location of crime scenes ((Inside or Outside).


Many serial offenders target prostitutes and their M.O. is simply to pose as a “John” in order to get their victims away from an area and into a comfort zone where they can act out their sexual fantasies. Richard Cottingham, who was a serial killer operating in both New York City Bergen County, New Jersey targeted prostitutes.  In some cases he would pick-up women in a New York City bar and slips a date-rape drug into their drinks. He would then take them to a New Jersey hotel where he would sexually assault and torture them. In some cases he left them nude and battered with burns on their breasts. In other incidents if he felt they could identify him he would kill them and leave their bodies in hotels in New York City and New Jersey.  He was a classic “Signature Killer” and all of crimes were linked through his signature behavior.


Other sexual offenders establish a casual relationship with a prospective victim that eventually allows them access to a victim’s home. Once the offender was in the victim’s residence he would sexually attack and kill them to prevent identification.


I consulted on one particular case where the offender had started out as a “Cat Burglar” who entered victim’s homes in the middle of the night to steal their valuables.  On one particular occasion he encountered a young women living alone. In a classic example of an opportunistic crime, he sexually attacked and raped her.  He then began to stalk and target women who lived alone. The burglary and thefts became secondary to his primary intention, which was to rape and sodomize his victims.   He was caught in one young woman’s home with his rape kit before he could assault her.  He was charged with Burglary and Attempted Rape. He pled guilty to the Burglary and was paroled.  Within two weeks of his parole he became a serial killer. He raped and sodomized four women during his home invasions to satisfy his lust and then killed them to prevent them from identifying him or ever being able to testify against him in court. .  He was also classic “Signature Killer” and all of crimes were linked by his specific type of binding the sexual activity, his DNA and his modus operandi.

The Signature Aspect of a violent sexual offender is a unique and integral part of the offender’s behavior, which refers to the psychodynamics of the event. The psychodynamics are the mental and emotional processes underlying human behavior and its motivations.


The “Signature” aspect is the end result of a number of biological, psychological and psychosocial factors that have combined to influence how an individual seeks sexual satisfaction or is able to sexually perform. The nucleus of the “Signature” element begins at an early age and is reinforced through repetitive fantasy, masturbatory activity and situational “acting-out” of these themes in various non-criminal scenarios.


Clinically speaking, there is a behavioral distinctiveness in human sexuality. This unique aspect of our arousal and response system accounts for why individuals differ in their sexual behaviors. In my textbook, Sex-Related Homicide and Death Investigation: Practical and Clinical Perspectives Second Edition[5] I devote an entire chapter on the investigative significance of fantasy in sex-related incidents.  Sexual fantasies play a major role in everyone’s sexual behavior. It is the drive factor for sexual expression.   The sexual offender and other individuals, who are aroused with thoughts and fantasies of sexual aggression, reinforce their beliefs through repetition illustrated by the use of sadistic pornography and fantasy drawings.  These serve as a form stimulus and excitement, a rehearsal before actually committing the offense or a mental re-creation of an actual event and represent the “Signature” component.


Fantasies may be used to organize a collection of deviant thinking into a criminal thought pattern referred to as Premeditation.   As a person fantasizes over time he feels the need to express these sexually violent Fantasies. Fantasy Drawings and Writings and Journals are excellent examples of premeditation and investigative evidence


Many Sexual Criminals are not just satisfied with the murder and have a compulsion to express themselves. Unlike M.O. the Core Signature is constant. However, over time the Signature Component evolves. Some examples are overkill, mutilation, sexually posing the body, engaging in post mortem activities. The victim is treated as a prop to be used to fulfill their violent sexual fantasies as they progress from victim to victim leaving their imprint at the scenes.


Dennis Rader, “The BTK Killer” would stalk his victims prior to the murders to ascertain when they would be alone. His M.O. was to cut the telephone wires at the victim’s home before entering.  He broke into some homes and waited for the victims to return. In one case he told his victims that he was on the run and needed cash. He told them he would only tie them up so he could make his getaway. In another case he pretended to be a student at Wichita State University and carried books to blend into the neighborhood. He also purported to be a detective and carried a briefcase to gain access to another victim’s home.  Rader also pretended to be an ADT inspector and a Southwest Bell telephone repairman. Although he used several different M.O.’s his “Signature” remained constant. In each of the cases he would bind, torture and kill his victims in a unique and distinctive manner with his bindings.  He strangled his victims to death both manually and with ligature. In one case he strangled the young woman unconscious and then brought her back and told her he was “BTK” as tightened the belt around to kill her. He would then communicate with authorities and taunt them with fantasy drawings and communications that he personalized with his BTK symbol.


He wrote, “How many do I have to kill before I get a name in the paper or some national attention…Yes the M.O. is different in each, but look a pattern is developing…The victims are tie up (sic) – most have been women-phone cut bring some bondage material-sadist tendencies..”[6]


Rader kept all of the color Polaroid™ photos of his victims along with his fantasy drawings and his original communications to authorities. He also kept “trophies” of his conquests in the form of jewelry and personal items taken from his victims so he could fantasize and re-live the murders in a secret location that he referenced  his “Mother Lode.” Dennis Rader’s activities are an excellent example of the “Signature” aspect of the violent sexual predator.


Offenders who engage in sexual activities do leave unique signatures, which allow law enforcement to link their crimes and similar events. Although the rituals may not be exactly the same or identical in nature the behavior of the offender with his victim and the sexual theme will be consistent.  The investigative question is, “What did the offender do that went beyond that necessary to commit the crime?”






As a homicide investigator you should focus on the similarities of cases as you develop an investigative hypothesis. If you have a second victim killed in a similar fashion with an M.O. and Signature that is consistent with the other case than you must think of the possibility of a serial killer.


Summation of Modus Operandi versus Signature

The Modus Operandi (M.O.) is the How?

      What did the offender do to accomplish the Act.

      What did he do to ensure the Success of the crime.

      What did he do to protect his identity and escape.

      M.O. is a thought-driven process based on past successes.


The Signature is the Why


      What did the offender do to the victim in the crime?

      What was the “Theme” of the event?

      Signature is a Fantasy-driven process

      These rituals are incorporated into the criminal act.

      What were the behavioral aspects to the event?



Geberth, V.J.  Practical Homicide Investigation: Tactics, Procedures and Forensic Techniques 5th Edition CRC

Press, LLC Boca Raton, FL, pp.595-597 and 1013-1016, 2015


Geberth, V.J. Practical Homicide Investigation: Tactics, Procedures and Forensic Techniques 4th Edition CRC Press,

LLC Boca Raton, FL, p.773, 2006.


Geberth, V.J. Crime Scene Staging: An Exploratory Study of the Frequency and Characteristics of Sexual

Posing in Homicides. Investigative Sciences Journal Vol2, Number 2 July, 2010.


Geberth, V.J. Sex-Related Homicide and Death Investigation:  Practical and Clinical Perspectives Second Edition,

CRC Press, LLC Boca Raton, Florida 2010, page, 606.




Vernon J. Geberth, M.S., M.P.S. who holds dual Master's Degrees is the author of Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques 5th Ed. CRC Press, LLC 2015. He retired from the NYPD as The Commanding Officer of The Bronx Homicide Task Force. These copyrighted materials have been excerpted with Geberth's permission. He can be reached at 

[1] Geberth, V.J. Practical Homicide Investigation: Tactics, Procedures and Forensic Techniques 4th Edition CRC Press, LLC Boca Raton, FL, p.773

[2] Geberth, V.J. Practical Homicide Investigation: Tactics, Procedures and Forensic Techniques 4th Edition CRC Press, LLC Boca Raton, FL, p.450.

[3] Geberth, V.J. Crime Scene Staging: An Exploratory Study of the Frequency and Characteristics of Sexual Posing in Homicides. Investigative Sciences Journal Vol2, Number 2 July, 2010

[4] Geberth, V.J. Practical Homicide Investigation: Tactics, Procedures and Forensic Techniques 4th Edition CRC Press, LLC Boca Raton, FL, p.455.


[5] Sex-Related Homicide and Death Investigation: Practical and Clinical Perspectives Second Edition, CRC Press, LLC Boca Raton, Florida 2010

[6] Geberth, V.J. Sex-Related Homicide and Death Investigation:  Practical and Clinical Perspectives Second Edition, CRC Press, LLC Boca Raton, Florida 2010, page, 606.