Collection and Preservation of Physical Evidence
in Sex-Related Death Investigations

By Vernon J. Geberth, M.S., M.P.S.
Author of Practical Homicide Investigation, Copyright 2003
Reprint: Law and Order, Vol. 51, No. 7, July, 2003
Article Expanded for Research Material

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The recovery and collection of evidence in sex-related homicide and death investigations is of paramount importance to the overall investigation. Although the general principles of collection, chain of custody and preservation remain the same, there are unique aspects to the types of evidence encountered in sex-related events. Sex-related homicides frequently result in various kinds of personal evidence including body fluids, such as semen, sperm, blood and saliva, as well as hairs and fibers and other microscopic evidence, which may be lost or contaminated due to any number of variables ranging from the dynamics of the event and the environment of the scene to the actions of police personnel at the scene. This article will focus on definitions and classifications of evidence, enhancement procedures to visualize certain types of evidence, and the practical application of the collection, chain of custody and preservation of evidence in sex-related homicide and death investigations. The article will conclude with a Sex-Related Crime Scene CHECKLIST excerpted from the author's book, Practical Homicide Investigation.

General Types of Evidence

In Practical Homicide Investigation each of these general types of evidence become crucial in the identification, apprehension and subsequent prosecution of offenders. However, the investigator should appreciate the nature of physical evidence.


Physical evidence is any tangible article, small or large, which tends to prove or disprove a point in question. It may be used to:

1.  Reconstruct the crime
2.  Identify the participants
3.  Confirm or discredit an alibi

The proper collection and disposition of physical or trace evidence from the crime scene and the body of the deceased is of the utmost importance to the investigation ad eventual court presentation. The evidence must have been obtained legally in order for it to be admissible. Therefore, it is imperative that both the legal authority to collect the evidence and the proper collection techniques be considered prior to the actual collection of the evidence. (See Law and ORDER Article entitled; PRACTICAL CRIME SCENE INVESTIGATION: Legal Considerations)

Classifications of Physical Evidence

Class Evidence

Class evidence is that which cannot be forensically identified with a specific source to the exclusion of all others. Examples are the non-DNA analysis of:


Individualistic Evidence

Individualistic evidence is evidence that can be positively and forensically identified with a specific source to the exclusion of all other sources. Examples are the DNA analysis of:



Is temporary in nature. Examples: Odors, Temperature, Imprints and indentations in soft or changing materials. (butter, wet sand, snow or mud.) Markings i.e. lividity, blood spatters on moveable objects.

Is produced by contact. Blood splatter, glass fracture patterns, fire burn patterns, Furniture position patterns, projectile trajectory, tire marks, M.O., clothing or article patterns, powder residue patterns.

Caused by an action or event. Lighting conditions at scene. Odor, color, direction of smoke. Flame (color, direction, temperature) Location of evidence in relation to the body. Vehicle (locked or unlocked; lights on or off, window open or closed, radio on or off, mileage)

Generally produced by physical contact of persons, objects, or between persons or objects. THE LINKAGE CONCEPT.

Practically speaking, there are two types of transfer evidence; trace transfer and pattern transfer evidence. Examples of' commonly encountered trace transfer evidence include hair, fibers, blood, semen, glass, and soil. Examples of pattern transfer evidence are imprint and impression evidence. Many times transfer evidence is a combination of trace and pattern components such as bloody shoeprints, hair and fibers, greasy fingerprints, or fabric impressions.

There is a principle in homicide investigation that refers to a theoretical exchange between two objects that have been in contact with one another. This theory of transfer or exchange is based on Locard's "Exchange Principle." Edmond Locard, a Frenchman, who founded the University of Lyons' Institute of Criminalistics, believed that whenever two human beings came into contact, something from one was exchanged to the other, and vice-versa. This exchange might involve, hairs, fibers, dirt, dust, blood and other bodily fluids, as well as skin cells, metallic residue and other microscopic materials. In Practical Homicide Investigation Locards' principle is summed up as follows:

1.  The perpetrator will take away traces of the victim and the scene.
2.  The victim will retain traces of the perpetrator and may leave traces of himself on the perpetrator.
3.  The perpetrator will leave behind traces of himself at the scene.

The goal is to establish a link between the various facets of the crime scene, the victim, physical evidence, and the suspect. All of these components must be connected for the successful resolution of the case. The LINKAGE CONCEPT rests on the principle of the "Theory of Transfer and Exchange." Remember: Anything and Everything may eventually become evidence.

A direct transfer occurs when materials are transferred from the original source to another person or object. An example would be a bleeding victim's blood found on the suspect or his clothing. Or, a latent fingerprint of the suspect discovered in the crime scene and/or the suspect's semen recovered from the victim.

An indirect transfer occurs when trace evidence, which was directly transferred to one location is then transferred again to another location. An example would be rug fibers at the crime scene, which had been transferred to the clothing of a victim, are then found in the suspect's car after he transported the body to the dumpsite.

Procedures for Collection of Evidence

In order to be introduced as physical evidence in a trial, an article must: Be properly identified Show a proper "Chain of Custody" Be material and relevant Meet all legal requirements:

The crime scene technician or crime scene investigator who is summoned to the scene should have operational supervision over gathering, collection, and marking of evidence for identification. However, the investigator assigned to the case is still in charge of the investigation and should be consulted prior to any evidence gathering or crime scene processing.

The proper collection and disposition of evidence will be accomplished if the following guidelines are adhered to:

  1. Each piece of evidence should be marked (on the container or item as applicable) to show its original position and location. This information should also be recorded in the investigator's notebook.
  2. Each article should be marked distinctively by the searching officer to identify the person who found the particular piece of evidence. In cases of small or fluid specimens this marking is done on the container.
  3. Each item should be described exactly and completely with the corresponding case numbers affixed and the date and time of collection indicated.
  4. Each item should be packaged in a separate, clean, and proper sized container to prevent cross?contamination or damage.
  5. Each package should be sealed to retain evidence and prevent any unauthorized handling.
  6. Each piece of evidence should show proper disposition:
         a. Police department laboratory
         b. Property clerk's office
         c. FBI Laboratory
  7. Proper records should be kept regarding each piece of evidence showing chain of custody. These records should reflect any movement of the evidence from the point of origin to its final disposition.

Remember, each item should be photographed before it is collected as evidence. These photographs should include a long-range view to show the relationship of the object to its surroundings and a close?range view to show the actual item being collected. (See Chapter 6 in Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques, 1996.


Tests for the Presence of Blood

This test is performed by rubbing a cotton swab that has been moistened in a saline solution on the suspected blood stain. A drop is added to the swab then a drop of hydrogen peroxide 3%. A positive reaction will turn swab PINK to RED within 15 seconds

This test is performed the same way as above. A positive reaction is indicated by a GREENISH-BLUE color that will appear almost immediately.

This reagent is sprayed onto the object to be checked. However, it must be viewed in total darkness. In positive reaction will luminesce VIOLET within 5 seconds.

This test is performed by rubbing a cotton swab that has been moistened in a saline solution on the suspected blood stain. A drop is added to the swab then a drop of hydrogen peroxide 3%. A positive reaction is indicated by an intense BLUE color.

Another in a series of presumptive tests that is specific for BLOOD. TMB is an enhancement reagent. The TETRA-METHYL BENZIDINE reacts with the HEME in the blood. Spray the surface lightly 2 to 3 times about 10 inches away from the surface. The Bloody Imprint Pattern should turn a Greenish-Blue. Over spray may give a very Dark BLUE pattern and mask ridge patterns.

This is a protein reactant, which does not ordinarily react with household cleaners like Luminol does. Hemaglow also glows brighter and can be photographed with a flat plane camera.

(LCV) A new positive blood identifier that turns permanent VIOLET when in contact with blood. Leucocrystal violet can be testified to in court as a blood identifier at the scene without further testing to identify the stain as blood.

Tests for the presence of Body Fluids

SEMEN Acid Phosphatase tests
SALIVA Amylase tests
URINE Creatinine, urea tests
FECAL MATTER Urobilinogen


Protein Enhancement Reagents

Ninhydrin detects trace amounts of amino acids associated with body secretions. The amino acids are transferred with the sweat from the pores of a finger, palm or the sole of the foot. Amino acids are easily absorbed into absorbent and partially absorbent surfaces such as paper, unfinished wood, cardboard, leather, etc.

Coomassie Blue is a general protein that works well with bloodstains. Coomassie is a more sensitive, general protein stain, than crystal violet stains.

Crystal violet works exceptionally well on adhesive surfaces such as tapes.

This is a protein reactant, which is sprayed onto the suspected area. NAPHTHOL, which is the AMIDO BLACK powder is mixed with Glacial Acetic Acid and Methanol. The formula is to mix 2 grams NAPHTHOL 100 ml Glacial Acetic Acid and 900 ml of Methanol.

THE PROCEDURE:  Set the prints with Methanol then spray the area with AMIDO BLACK. Rinse with 100 ml Glacial Acetic Acid and 900 ml of Methanol. Rinse with water. Clean with Clorox.

Fatty Acid, Elements and compounds Enhancement Reagents

SUPERGLUE (Cyanoacrylate) FUMING

Method for Diagnosing Abrasions, Lacerations and Other Skin Disruptions in the Perineum and Perianal Areas.

According to Dr, Frederick T. Zugibe, Chief Medical Examiner, Rockland County, New York, an excellent procedure in determining sexual assault injuries can be visualized by the application of Toluidine Blue in .01% solution and/or Methylene Blue or Azure. Toluidine stains ground substance or mucopolysaccharides, which are found in abrasions as well as other skin injuries. The intact skin will not stain but injured skin will be visualized with the application of Toluidine Blue and/or Methylene Blue or Azure. This test is extremely effective in child sexual abuse cases. It can also be administered by doctors in Hospital Emergency Rooms, who treat live victims of sexual assault to document the presence of mucopolysaccharides. A simple color Polaroid taken before and after the application produces excellent documentation of sexual abuse, which can be used in trial. Toluidine Blue is applied with cotton or gauze to the area of suspected trauma. The excess is wiped-off with a K-Y jelly or similar substance. The stain will remain in the area of trauma.


In sex-related homicide cases, basic evidence collection procedures acquire an increased importance. Human behavior patterns and psychosexual activities, not generally amenable to ordinary collection techniques become additional factors to consider in determining the reason and motive for the killing. Practical experience in homicide investigation coupled with an understanding of human behavior patterns and human sexuality are important prerequisites in analyzing these types of cases.

These copyrighted materials have been excerpted with permission of the author from Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques Third Edition 1996 CRC Press, LLC and Sex-Related Homicide and Death Investigations: Practical and Clinical Perspectives (In Press).

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