Week 4 Lecture
Physical Evidence and the Crime Scene
The role of physical evidence at a crime scene is a critical one for it can aid in the identification of a perpetrator, as well as the prosecution of that perpetrator. It can also help investigators determine what happened. Physical evidence can be biological in nature or take other forms, such as tool marks, fingerprints, bite marks, or ballistics, among others. Despite some limitations, these pieces of evidence can be incredibly powerful investigative tools.
An investigator must expect to find evidence upon entering a crime scene and only has one shot to get it right. Thus, the collection and documentation of physical evidence at a crime scene must be done thoroughly and carefully. All crime scene procedures are to be followed to ensure the integrity of the evidence collected.
The Role of Physical Evidence in the Criminal Investigative Process
Roles of physical evidence
Physical evidence can help establish the elements of a crime and, thus, function as corpus delicti evidence. However, it is not necessary that physical evidence be present in order to establish that a crime occurred.
- Physical evidence can be used to make associations between crime scenes, perpetrators, victims, and tools. This is the most common role of physical evidence.
- Physical evidence can function as corroborative evidence and thereby support other evidence in establishing a fact in question.
- Physical evidence may serve an identification function. It can be direct or circumstantial in establishing a fact.
Physical evidence is not especially effective at identifying a perpetrator if the perpetrator is not already known. Other evidence and circumstances often leads to the identity of the perpetrator.
The Crime Scene and its Management
A crime scene is the area within the immediate location in which the crime occurred.
A secondary crime scene is an area where significant evidence relating to a crime is found, but not where the crime actually occurred.
Arriving at the Scene: Initial Response/Prioritization of Efforts
Crime scene procedures:
- Secure the crime scene to minimize contamination by external factors that could lead to the destruction of evidence.
- Determine the legality of entering and searching the crime scene. There is not a crime scene exception to the search warrant requirement; an officer needs probable cause, a warrant, or some other exception.
- Determine officer safety.
- Summon medical attention for injured parties, if necessary.
- Crime scene must constantly be protected from persons at or near the scene.
- Establish the boundaries of the crime scene to protect it.
- Initial responding officers should brief the investigators taking charge of the investigation, if necessary.
- All activities and observations of the responding officers should be recorded in the required reports as soon as possible.
Preliminary Documentation and Evaluation of the Scene
The responsibilities of the investigators in charge of the crime scene:
- Assess the crime scene for safety and boundaries.
- Separate suspects, witnesses, and victims to be monitored.
- Designated personnel should interview these individuals as soon as possible.
- Determine the legality of obtaining a search warrant.
- A path of entry and movement for personnel should be established.
- Determine the need for additional investigative resources.
- Search for and locate additional witnesses who may not have been present at the scene through a neighborhood canvass. A neighborhood canvass involves the door-to-door questioning of residents who live near the crime scene.
Processing the Information
- Determine who is responsible for what and establish the composition of the investigative team.
- The investigator in charge requires that all personnel follow procedures to ensure safety and the integrity of all recovered evidence.
- The investigator in charge must be responsible for or supervise the taking of photos, videos, sketches, measurements, and notes.
a. Crime scene sketches are either hand-drawn or computerized and should be as detailed as possible.
i. Sketches should include date, time, and location as well as weather/lighting conditions, identity of personnel, dimensions, distances, measurements, scale, key, legend, and compass orientation.
b. Photographs should tell a story and all conditions in which the photos were taken should be recorded.
- The investigator in charge should determine the order in which physical evidence is collected, as some evidence is more vulnerable to alteration or destruction.
- The investigative team should ensure the proper collection, preservation, packaging, and transportation of evidence.
Methods of conducting a search for evidence can include a grid, strip, and spiral search.
Locard’s Exchange Principle holds that any time a person comes into contact with a person or place, something from that person is left behind or something of that place is taken with the individual.
- This is valid, but a better principle is simply “expect to find evidence.”
Types of Physical Evidence
Class characteristic evidence (can the evidence be associated with a particular group?) has characteristics common to a class or group.
Individual characteristic evidence (can the evidence be associated with a particular person?) has characteristics that can be identified as originating from a particular source.
- Blood consists of red and white blood cells located in the plasma. It can be grouped into four types: type A, type B, type O, type AB. It can be found virtually anywhere in crime scenes and is most commonly found at serious crimes like homicide and assault.
- Semen is a seminal fluid that contains sperm. It is often found as a result of sexual crimes.
- Human saliva consists mostly of water, but also contains mucus, proteins, enzymes, and skin cells. It is commonly found on cigarette butts, bite marks, bottles, cans, clothing, envelopes, and stamps.
- Hair consists of the outer core of cells, known as the cuticle, the cortex, and the medulla. Hair is most commonly found in violent crime scenes like homicide and assault, where a struggle took place. Hair can be found on clothing, washing machines, sinks, vehicles, and many other locations.
DNA Analysis (printing) and Its Impact on the Usefulness of Biological Evidence
DNA is the genetic building block of all living things and is found in virtually every cell in the human body. No two people (except for identical twins) share the same DNA.
DNA analysis can be used to positively identify a suspect as a perpetrator or exclude a suspect as a perpetrator. DNA can also be used to confirm the identity of victim.
Other Types of Physical Evidence
- Fingerprints consist of ridges, depressions, and separations. They are unique to an individual and remain unchanged throughout one’s life. Fingerprints can be classified into certain patterns: loops, whorls, and arches. The most common type of fingerprint is loops.
- There are three types of fingerprints that can be recovered from a crime scene: visible transferred prints, visible impression prints, and latent prints.
- AFIS (Automated Fingerprint Identification System) stores collected fingerprints to help identify perpetrators. One AFIS finds several “hits” that then are manually compared for any unique characteristics.
- Shoe Prints, Impressions, and Tire Tracks
- Shoe prints are created when material from the bottom of shoes is transferred to another surface, leaving an outline of the bottom of the shoe.
- Shoe impressions and tire tracks are left in a soft material, commonly mud or snow.
- A tool mark is any mark created by an instrument or tool when it comes into contact with another surface.
Bite Marks and Dental Evidence
- This can be powerful evidence because each individual has a unique set of teeth in terms of form, arrangement, spacing, dental work, and bite.
- Dental evidence is helpful in identification.
What gun evidence can be collected and examined?
- The gun itself is useful in order to determine its function, general condition, and any alterations that may have been made.
- The trigger-pull can be examined for the amount of force necessary to set off the gun.
- Fired bullets can be examined for their caliber and manufacturer.
- Casings can be examined to determine caliber and manufacturer.
- Gunshot residue is the most commonly examined firearm evidence because it can often determine who fired the weapon as well as how far away the victim was from the perpetrator.
- Fiber is found in textiles and fabrics. Fiber can be natural or synthetic and can be transferred easily from one surface to another.
- Soil contains both man-made materials and organic materials. It is commonly found on the bottom of people’s shoes.
- Soil can be examined through color, texture, and composition comparison or through a density gradient tube.
- Paint is a colored polymer that is applied to and adheres to certain surfaces. It can be transferred from one surface to another, wet or dry.
Blood Pattern Analysis
- Bloodstain patterns can help in the understanding of how a crime occurred.
- Computers, cell phones, and GPS devices provide a wealth of information regarding communications, schedules, travels, and criminal behaviors.
- Videos can be potentially very powerful evidence if the crime being investigated was documented in this way.
Questioned Documents / Handwriting Analysis
- Written documents can be examined by their content, their actual style and mechanics, and their penmanship. The paper and ink can also be analyzed. Also, documents copied, scanned, printed, or typewritten can be analyzed for their producer and their make and model.
- Drugs are commonly seized evidence and come in various forms, including pills, powder, and several other forms.
The Role of Crime Laboratories in Criminal Investigations
- While evidence is collected at crime scenes, it is analyzed in laboratories most of the time.
- There are both public and private facilities. The most commonly performed test is DNA testing.
- A huge problem associated with crime laboratories is the sizable backlog they face.