9.5: Physical Evidence
The court will also generally attribute a high probative value to physical exhibits. The court likes physical evidence because they are items the court can see and examine to interpret the facts in issue for proof beyond a reasonable doubt. Physical evidence can include just about anything, such as weapons, fingerprints, shoe prints, tire marks, tool impression, hair, fiber, or body fluids. These kinds of physical exhibits of evidence can be examined and analyzed by experts who can provide the court with expert opinions that connect the item of evidence to a person, place, or the criminal event. This allows the court to consider circumstantial connections of the accused to the crime scene or the accused to the victim. For example, in the case where the fingerprints of a suspect are found at a crime scene, and a DNA match of a murder victim’s blood is found on that suspect’s clothing, forensic connections could be made and, in the absence of an explanation, the court would likely find this physical evidence to be relevant and compelling evidence with high probative value.
Types of Physical Evidence
- Fingerprints
- Shoe Prints
- Tire Tracks
- Firearms (bullets, bullet casings)
- Hair (may contain DNA)
- Fibers
- Body Fluid (blood, semen, saliva) - all containing DNA
Crime Scene Management
Crime scene management skills are an extremely significant task component of investigation because evidence that originates at the crime scene will provide a picture of events for the court to consider in its deliberations. That picture will be composed of witness testimony, crime scene photographs, physical exhibits, and the analysis of those exhibits, along with the analysis of the crime scene itself. From this chapter, you will learn the task processes and protocols for several important issues in crime scene management. These include
- Note taking
- Securing a crime scene
- Evidence management
- Scaling the investigation to the event
Note Taking
Although other documents will be created by the investigator to manage the crime scene, no other document will be as important to the investigator as the notebook. The notebook is the investigator’s personal reference for recording the investigation.
Many variations of police notebooks have emerged over the years. The court will sometimes even accept police notes that have been made on a scrap of paper if that was the only paper available at the time. However, beyond extreme circumstances, in operational investigations, the accepted parameters of a police notes and notebooks are:
- A book with a cover page that shows the investigators name, the date the notebook was started, and the date the notebook was concluded
- Sequential page numbers
- A bound booklet from which pages cannot be torn without detection
- Lined pages that allow for neat scripting of notes
- Each entry into the notebook should start with a time, date, and case reference
- Blank spaces on pages should not be left between entries and, if a blank space is left, it should be filled with a single line drawn through the space or a diagonal line drawn across a page or partial page space
- Any errors made in the notebook should only be crossed out with a single line drawn through the error, and this should not be done in a manner that makes the error illegible.
In court, the investigator’s notebook is their best reference document. When testifying, the court will allow an investigator to refer to notes made at the time to refresh their memory of events and actions taken. When an investigator’s notebook is examined by the court, notes consistent with the investigator’s testimony provide the court with a circumstantial assurance or truthfulness that the evidence is accurate and truthful (McRory, 2014). Alternately, if critical portions of the investigation are not properly recorded or are missing from the notebook, those portions of the evidence will be more closely scrutinized by the defense. The court may give those unrecorded facts less weight in its final deliberations to decide proof beyond a reasonable doubt.
Integrity of the Crime Scene
As part of crime scene management, protecting the integrity of the crime scene involves several specific processes that fall under the Tasks category of the STAIR Tool. These are tasks that must be performed by the investigator to identify, collect, preserve, and protect evidence to ensure that it will be accepted by the court. These tasks include:
- Locking down the crime scene
- Setting up crime scene perimeters
- Establishing a path of contamination
- Establishing crime scene security
When an investigator arrives at a crime scene, the need to protect that crime scene becomes a requirement as soon as it has been determined that the criminal event has become an inactive event and the investigator has switched to a strategic investigative response. As you will recall from the Response Transition Matrix, it is sometimes the case that investigators arrive at an active event in tactical investigative response mode. In these cases their first priority is to protect the life and safety of people, the need to protect the crime scene and its related evidence is a secondary concern. This is not to say that investigators attending in tactical investigative response mode should totally ignore evidence or should be careless with evidence if they can protect it; however, if evidence cannot be protected during the tactical investigative response mode, the court will accept this as a reality.
Evidence Management
The STAIR tool (See graphic below) provides the process used in crime scene management. It is the analysis and process that must occur to establish connections between the victims, witnesses, and suspects in relation to the criminal event. The crime scene is often a nexus of those events and consequently, it requires a systematic approach to ensure that the evidence gathered will be acceptable in court.
Exhibits, such as blood, hair, fiber, fingerprints, and other objects requiring forensic analysis, may illustrate spatial relationships through evidence transfers. Other types of physical evidence may establish timelines and circumstantial indications of motive, opportunity, or means. All evidence within the physical environment of the crime scene is critically important to the investigative process. At any crime scene, the two greatest challenges to the physical evidence are contamination and loss of continuity.
Contamination of Evidence
Contamination is the unwanted alteration of evidence that could affect the integrity of the original exhibit or the crime scene. This unwanted alteration of evidence can wipe away original evidence transfer, dilute a sample, or deposit misleading new materials onto an exhibit. Just as evidence transfer between a suspect and the crime scene or the suspect and the victim can establish a circumstantial connection, contamination can compromise the analysis of the original evidence transfer to the extent that the court may not accept the analysis and the inference that the analysis might otherwise have shown.
Scaling the Investigation to the Event
Not every crime scene is a major event that requires an investigator to call out a team and undertake the crime scene and evidence management processes that have been described in this book. Often, for minor crimes, a single investigator will be alone at the crime scene and will engage in all the roles described, albeit on a far smaller scale. When this process is being undertaken by a single investigator on a smaller scale, the issues of diagram, security log, and exhibit log may be limited to data and illustrations in the notebook of the investigator.
It is important to stress that each of the tasks below needs to be considered and addressed for every crime scene investigation, no matter how big or how small. Specifically:
- The crime scene must be secured, preserved, and recorded until evidence is collected
- Existing contamination must be considered and recorded
- Cross-contamination must be prevented
- Exhibits must be identified, preserved, collected, and secured to preserve the chain of continuity.
Large scale or small scale, all these issues must be considered, addressed, and recorded to satisfy the court that the crime scene and the evidence were handled correctly.
Figure 9.2 The Forensic Examination Process
Figure 9.3 Diagram of the Transfer Theory
Figure 9. 4 The Stair Tool guides the investigative process