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Executive Summary:

Violent Crime has increased dramatically in the United States in the past 50 years. Many of these crimes involve serial homicide and rape which are especially challenging for investigators and experts since the perpetrators are usually experienced at what they do and don't leave many clues at the crime scene (if it can even be found). Plus, these crimes have a tendency to gain a lot of notoriety from the news media and public which results in intense pressure on the police department or investigating agency to solve these crimes quickly. The Serial Homicide and Rape Matrix may be helpful in these types of cases since the Matrix allows the comparison of many factors and may reveal information that can speed the arrest of the perpetrator.

Background:

Violent crime (murder, rape, robbery, and aggravated assault) in the United States has increased 493% from 1960 through 2011. The population has increased 174% during the same period.

FBI Crime Clock for 2011:

One Murder every 36 minutes.
One Forcible Rape every 6.3 minutes.
One Robbery every 1.5 minutes.
One Aggravated Assault every 42 seconds.
One Burglary every 14.4 seconds.
One Larceny Theft every 5.1 seconds.
One Motor Vehicle Theft every 44.1 seconds.

The Matrix:

The Matrix is a simple device that can be used to compare many factors in a serial homicide, rape, or any other type of serial crime. It is basically a spreadsheet setting forth factors about each crime. The investigator/expert may want to list date, time, address, entry, weapon, key words said to the victim, injuries and anything else that he/she thinks is important. These spreadsheets are only limited by the imagination of the investigator or expert. However, too many factors may make the spreadsheet too complex to be useful so I suggest that the initial document list only the major factors in each crime. The spreadsheet can then be expanded as more information is developed.

Example:

A serial rapist operating in the same city commits several crimes and always uses the same Method of Operation.

  1. Enters residences between the hours of midnight and 6:00 am.
  2. Brings a knife to the scene and takes it with him.
  3. Uses similar words when confronting the victim.
  4. Chooses homes or apartments occupied by single females.
  5. Gains access by prying open a window.
  6. Threatens to return if victim contacts police.
  7. Prefers a certain type of sexual activity with the victim.
  8. Commits or attempts to commit a rape every 10 to 14 days.
  9. Always has an odor of alcohol.
  10. Rapist fits the same general description in each crime.

The matrix for these crimes would be set up as follows. Across the top of the spreadsheet would be Date, Time, Location, Weapon, Means of Entry, Words Used with Victim, Type of Sexual Activity Preferred, Threats, Description, etc. The left column would list each crime by victim name.

The value of the matrix in this case is to identify the rapist as the same individual in each case. The matrix will also indicate when the rapist might make another rape attempt. Police can then be alert when they think the rapist might strike again and send unmarked police vehicles to the area where they think the rapist may be operating.

Further, the address of each attack should be marked on a map of the city showing first known attack to the most recent to see if there is any pattern to the assaults. In many cases, the first rape by the perpetrator will be close to his residence or place of work and then move out as he gains confidence. Also, a map depiction of each assault may indicate that the offender prefers a certain area of the city or has a certain pattern that he follows. A good source for this technique is Geographic Profiling by D. Kim Rossmo, CRC Press, 1999. Chapter 7, "Geography of Crime" is very instructive.

Always keep an open mind in these cases and do not assume that the rapist is using a vehicle. He may be using public transportation, a bicycle, or walking to the crime scenes if they are close to his residence. If stopped by the police while traveling to his crime scene via bicycle or on foot, he will say that he could not sleep so thought he would get some exercise. A review of Field Identification reports may show that the offender has been stopped on several occasions during the hours when the assaults have taken place.

A second matrix should be set up in order to compare victims to see if they have anything in common. Again, across the top would be date, time, address, victim age, victim employment, height, weight, hair color, eye color, or anything else that the investigator thinks might be important. The matrix is only limited by the imagination of the investigator(s). Each victim would be listed in order down the left side of the matrix spreadsheet. Photos of each victim should also be obtained and reviewed for anything the victims may have in common (e.g. length of hair, hair style, tattoos etc.)

Conclusion:

The Serial Homicide and Rape Matrix utilizes standard spreadsheet software to analyze serial homicides and rapes. The spreadsheets are easy to set up and will many times provide clues which become very obvious when placed in a spreadsheet format. The matrix may be helpful in linking crimes and indicating whether or not you have a serial offender. The spreadsheets are very beneficial for small departments which have limited funds for computer software. The matrix may be used in any type of serial crime: homicide, rape, robbery, burglary, etc.

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Dan L. Vogel is Forensic Consultant Expert Witness based in Oklahoma City. He has 27 years of Federal law enforcement experience and has testified as an expert in Federal and state court. Pro Bono work is performed on a case by case basis. He is currently a member of the Consulting Committee, The American Investigative Society of Cold Cases. dvogel1@cox.net

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