Forensic Evidence Management: From the Crime Scene to the Courtroom provides best practices policies for forensic science entities and their employees to maintain chain of custody and evidence integrity throughout the course of evidence collection, storage, preservation, and processing.
Forensic Evidence Management: From The Crime Sc...
The focus of the book will be to address the issues related with evidence handling and analysis inside the forensic laboratory, in particular, and to offer best practices and guidelines from leading forensic experts in the field. Forms of evidence covered include biological, chemical, trace, firearm, toolmark, fingerprint, and a host of others types recovered at crime scenes. The book concludes with a chapter on ethics, bias, and ethical practices in evidence handling in the field and laboratory analysis.
Forensic Evidence Management: From the Crime Scene to the Courtroom provides best practices policies for forensic science entities and their employees to maintain chain of custody and evidence integrity throughout the course of evidence collection, storage, preservation, and processing.
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:
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:
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.
As soon as the event transitions to an inactive event with a strategic investigative response, the expectations of the court, regarding the protection of the crime scene and the evidence, will change. This change means that there is an immediate requirement for the investigator to take control of and lock down that crime scene.
Very often, when the change to strategic investigative response is recognized, first responders and witnesses, victims, or the arrested suspect may still be inside the crime scene at the conclusion of the active event. All these people have been involved in activities at the crime scene up to this point in time, and those activities could have contaminated the crime scene in various ways. Locking down the crime scene means that all ongoing activities inside the crime scene must stop, and everyone must leave the crime scene to a location some distance from the crime scene area. Once everyone has been removed from the crime scene, a physical barrier, usually police tape, is placed around the outside edges of the crime scene. Defining of the edges of the crime scene with tape is known as establishing a crime scene perimeter. This process of isolating the crime scene inside a perimeter is known as locking down the crime scene.
The crime scene perimeter defines the size of the crime scene, and it is up to the investigator to decide how big the crime scene needs to be. The size of a crime scene is usually defined by the area where the criminal acts have taken place. This includes all areas where the suspect has had any interaction or activity within that scene, including points of entry and points of exit. The perimeter is also defined by areas where the interaction between the suspect and a victim took place. In some cases, where there is extended interaction between a suspect and a victim over time and that activity has happened over a distance or in several areas, the investigator may need to identify one large crime scene, or several smaller crime scene areas to set crime scene perimeters. Considering the three stages of originating evidence, an investigator may find that pre-crime or post-crime activity requires the crime scene perimeter to surround a larger area, or there maybe even be an additional separate crime scene that needs to be considered.
It is not possible to eliminate all potential contamination of a crime scene. We can only control and record ongoing contamination with a goal to avoid damaging the forensic integrity of the crime scene and the exhibits. Once a crime scene has been cleared of victims, witnesses, suspects, first responders, and investigators, it is necessary to record, in notes or a statement from each person, what contamination they have caused to the scene. The information being gathered will document what evidence has been moved, what evidence has been handled, and by whom. With this information, the investigator can establish a baseline or status of existing contamination in the crime scene. If something has been moved or handled in a manner that has contaminated that item before the lock down, it may still be possible to get an acceptable analysis of that item if the contamination can be explained and quantified.
With everyone now outside the crime scene and the perimeter locked down, the next step is to establish a designated pathway where authorized personnel can re-enter the crime scene to conduct their investigative duties. This pathway is known as a path of contamination and it is established by the first investigator to re-enter the crime scene after it has been locked down. Prior to re-entering, this first investigator will take a photograph showing the proposed area where the path of contamination will extend, and then, dressed in the sterile crime scene apparel, the investigator will enter and mark the floor with tape to designate the pathway that others must follow. In creating this pathway, the first investigator will avoid placing the pathway in a location where it will interfere with apparently existing evidence and will place it only where it is required to gain a physical view of the entire crime scene. As other investigators and forensic specialists enter the crime scene to perform their duties, they will stay within the path of contamination and, when they leave the path to perform a specific duty of investigation or examination, they will record their departure from the path and will be prepared to demonstrate their departure from the pathway and explain any new contamination caused by them, such as dusting for fingerprints or taking exhibits.
At the same time the crime scene is being defined with perimeter tape, it is also necessary to establish a security system that will ensure that no unauthorized person(s) enters the crime scene and causes contamination. For this purpose, a crime scene security officer is assigned to regulate the coming and going of persons from that crime scene. For the assigned security officer, this becomes a dedicated duty of guarding the crime scene and only allowing access to persons who have authorized investigative duties inside the crime scene. These persons might include:
As we have already learned in the STAIR tool, analysis is the 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, fibre, 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 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.
38c6e68cf9