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Chapter 2: Crime Scene Investigation
2.1: Crime Scene
Crime Scene – the center of the forensic world, where everything starts, and the foundation upon which all subsequent analyzes are based.
The processing of a crime scene is a method of “careful destruction”: It is a one-way street, and one can never go back and undo an action.
Standard operating procedures and protocols guide the crime scene investigator (CSI), providing a framework for comprehensive and accurate evidence collection, documentation, and transmission to the laboratory.
2.2: Artifacts and Evidences
Crime scenes and archaeological sites are made up of the physical remains of past human activity and, in a sense, are snapshots of the “leftovers” of a completed process.
All the information, the relationships, the context of the items must be documented as they are destroyed to allow for some level of reconstruction in the laboratory or museum.
Datum – a fixed reference point for all three dimensional measurements.
It should be something permanent, or nearly so, like a light switch, a tree, or a post.
Artifact – a human-made or modified portable object.
Feature – a non-portable artifact, such as a fire pit, a house, or a garden.
Organic or environmental remains – natural remnants that nonetheless indicate human activity, such as animal bones or plant remains but also soils and sediments.
Provenance – the origin and derivation of an item in three-dimensional space, in relation to a datum and other items.
Evidence can be defined as information, whether personal testimony, documents, or material objects, that is given in a legal investigation to make a fact or proposition more or less likely.
2.3: Crime Scene Investigation
First on the Scene
The success of any crime scene investigation depends in large part on the actions taken in the first few minutes after the First Officer (or FO) or CSI arrives.
The primary task of the FO at a crime scene is to secure the scene and prevent destruction or alteration of the critical and sometimes fragile context of a crime scene. The assumption is that the perpetrator has left physical evidence at the crime scene.
The FO’s duties are simple in concept but complex in execution:
Detain any potential suspects.
Render medical assistance to those who need it.
Do not destroy, alter, or add any evidence at the scene.
Prevent others, even superiors, from doing the same.
Once the immediate scene is secured, the lead investigator further defines and evaluates the scene.
Plan of Action
Preparation
The officers or investigators assigned to the scene should have obtained a search warrant, if necessary, by the time the crime scene processing begins.
The search should be discussed with involved personnel before arriving at the scene.
A command station for communication and decision-making should be established in an area away from the scene but still within the secured perimeter.
Communication between the various agencies’ representatives, such as medical examiners, laboratory personnel, emergency medical technicians, and attorneys, is crucial to a smooth and successfully executed crime scene process.
Think ahead. Fifteen minutes of thought can save hours, and possibly lives, later on. Prepare the paperwork to document the search before searching.
Secure the Scene, Secure Items
If the FO hasn’t done so, take control of the scene immediately.
Determine the extent to which the scene has, or has not, been protected.
Talk to personnel who have knowledge of the original condition.
Keep out unauthorized personnel.
Record who enters and leaves, even if they are an agency’s superiors.
It is important to remember the central nature of crime scene notes.
The adage from quality assurance, “if it is not written down, it didn’t happen,” is a good guide on what to record.
Securing the scene is so critically important that we cannot overstate this point.
Preliminary Survey
The survey is an organizational stage to plan for the search.
Take preliminary photographs to establish the scene and delineate the extent of the search area.
Make note of special “problem” areas, such as tight spaces, complex evidence arrangements, or environments with transient physical evidence (blood in a running shower, for example).
Take extensive notes to document the scene, physical and environmental conditions, and personnel tasks and activities.
The easily accessible areas are processed first, but then move on to out-of-the-way locations, like in cupboards, under rugs or carpeting, or in drawers.
Look for hidden items, secret compartments, and false fronts.
Another important reminder is that the scene may not even be the scene—the scene may be contrived to look like an accident or some other type of crime.
Photography
The photographic log documents all the photographs taken and a description and location of what’s in the photograph.
A progression of establishing (overall or perspective views), medium (within 6 ft), and close-up (within 12 in) views of the crime scene should be collected.
Multiple views, such as eye level, top, side, and bottom, help to represent what the scene or a piece of evidence looked like in place.
Start with the most fragile areas of the crime scene first; move through the scene as evidence is collected and processing continues.
Document the process itself, including stages of the crime scene investigation, discoveries, and procedures.
Photographs must at least be taken before the evidence is recovered.
Photographs that include a scale should also have the photographer’s initials and the date. This is easily accomplished by using a disposable plastic ruler and writing the pertinent information (case number, item number, etc.) on it with a permanent marker.
Photograph the crime scene in an overlapping series using a wide-angle lens, if possible; 50mm lenses are the standard issue for cameras—use both and lots of film.
Sketch
Distances, angles, time, temperature—all these elements make the crime scene sketch. A sketch should include the following:
The case identifier
Date, time, and location
Weather and lighting conditions
Identity and assignments of personnel
Dimensions of rooms, furniture, doors, and windows
Distances between objects, persons, bodies, entrances, and exits
An arrow pointing toward magnetic north
Chain of Custody
This form helps document the movement of evidence from the time it is obtained to the time it is presented in the court.
The most compelling evidence in the world can be rendered useless if inaccuracies or gaps exist in a chain of custody.
Crime Scene Search and Evidence Collection
Be alert for all evidence: The perpetrator had to enter or exit the scene!
Mark evidence locations on the sketch and complete the evidence log with notations for each item of evidence.
e. If possible, having one person serving as evidence custodian makes the collection more regular, organized, and orderly. Again, if possible, two persons should observe evidence in place, during recovery, and be marked for identification. Use tags, or if feasible, mark directly on the evidence.
Wear gloves to avoid leaving fingerprints — but be aware that after about 30min, it is possible to leave fingerprints through latex gloves.
Evidence should not be handled excessively after recovery. Seal all evidence packages with tamper-evident tape at the crime scene.
Simple geometry can help locate and reconstruct where things were in a sketch.
Triangulation – the process of finding a distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other reference points.
Final Survey
A final survey is recommended to review all aspects of the search.
Discuss the search and ask questions of each other.
Read over the paperwork for a final check for completeness.
Take photographs of the scene showing the final condition.
Secure all evidence and retrieve all equipment.
A final walk-through with at least two people from different agencies (if possible) as a check on completeness is a must.
Submission of Evidence to the Laboratory
The collected evidence may be submitted to the laboratory by that agency’s personnel (that is, laboratory personnel) or by CSIs or law enforcement officers.
A form is typically filled out or a letter written detailing what is submitted, under what criminal circumstances, who is submitting the items, and what laboratory examinations are requested.
2.4: Safety
Walking into a crime scene is one of the most hazardous activities a forensic scientist or CSI can do. Chemical and biological threats abound, not to mention knives, firearms, explosives… the list goes on.
The increase in bloodborne pathogens (BBPs) and other pathogens that may be encountered at crime scenes has made law enforcement and CSIs more aware of personal protection when responding to crime scenes.
Sources and Forms of Dangerous Materials
Inhalation:
Airborne contaminants can occur as dust, aerosol, smoke, vapor, gas, or fume. Immediate respiratory irritation or trauma might ensue when these contaminants are inhaled; some airborne contaminants can enter the bloodstream through the lungs and cause chronic damage to the liver, kidneys, central nervous system, heart, and other organs.
Skin Contact:
A frequent route of contaminant entry into the body. Direct effects can result in skin irritation or trauma at the point of contact, such as a rash, redness, swelling, or burning.
Ingestion:
A less common route of exposure. Ingestion of a corrosive material can cause damage to the mouth, throat, and digestive tract. When swallowed, toxic chemicals can be absorbed by the body through the stomach and intestines.
Injections:
Needlesticks and cuts from contaminated glass, hypodermic syringes or other sharp objects can inject contaminants directly into the bloodstream. Extreme caution should be exercised when handling objects with sharp or jagged edges.
2.5: Universal Precautions
These measures require employees to treat all human blood, body fluids, or other potentially infectious materials as if they are infected with diseases such as hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV).
The following protective measures should be taken to avoid direct contact with these potentially infectious materials:
Use barrier protection such as disposable gloves, coveralls, and shoe covers when handling potentially infectious materials. Gloves should be worn, especially if there are cuts, scratches, or other breaks in the skin.
Change gloves when torn, punctured, or when their ability to function as a barrier is compromised.
Wear appropriate eye and face protection to protect against splashes, sprays, and spatters of infectious materials. Similar precautions should be followed when collecting dried bloodstains.
Place contaminated sharps in appropriate closable, leak-proof, puncture-resistant containers when transported or discarded. Label the containers with a BIOHAZARD warning label. Do not bend, recap, remove, or otherwise handle contaminated needles or other sharps.
Prohibit eating, drinking, smoking, or applying cosmetics where human blood, body fluids, or other potentially infectious materials are present.
Wash hands after removing gloves or other personal protective equipment (PPE). Remove gloves and other PPE in a manner that will not result in the contamination of unprotected skin or clothing
Decontaminate equipment after use with a solution of household bleach diluted 1:10, 70% isopropyl alcohol, or another disinfectant. Noncorrosive disinfectants are commercially available. Allow sufficient contact time to complete disinfection.
2.6: Personal Protective Equipment
Hand Protection
Nitrile gloves provide protection from acids, alkaline solutions, hydraulic fluid, photographic solutions, fuels, aromatics, and some solvents.
Neoprene gloves offer protection from acids, solvents, alkalies, bases, and most refrigerants.
Polyvinyl chloride is resistant to alkalies, oils, and low concentrations of nitric and chromic acids.
Latex or natural rubber gloves resist mild acids, caustic materials, and germicides.
Gloves should be inspected for holes, punctures, and tears before use.
If a glove is torn or punctured, replace it. Remove disposable gloves by carefully peeling them off by the cuffs, and slowly turning them inside out. Discard disposable gloves in designated containers and, it should go without saying, do not reuse them.
Eye Protection
Safety glasses and goggles should be worn when handling biological, chemical, and radioactive materials.
Face shields can offer better protection when there is a potential for splashing or flying debris. Face shields alone are not sufficient eye protection; they must be worn in combination with safety glasses.
Contact lens users should wear safety glasses or goggles to protect their eyes. Protective eyewear is available for those with prescription glasses and should be worn over them.
Foot Protection
Shoes that completely cover and protect the foot are essential – no sandals or sneakers!
Protective footwear should be used at crime scenes when there is a danger of foot injuries due to falling or rolling objects or to objects piercing the sole and when feet are exposed to electrical hazards.
Shoe covers can provide protection to shoes and prevent contamination to the perimeter and areas outside the crime scene.
Other Protection
Certain crime scenes, such as bombings and clandestine drug laboratories, can produce noxious fumes requiring respiratory protection.
In certain crime scenes, such as bombings or fires where structural damage can occur, protective helmets should be worn.