7.2: PROCESSING THE CRIME SCENE

From this chapter, you will learn the task processes and protocols for several important issues in crime scene management. These include: Locking down the crime scene, setting up crime scene perimeters, protecting the evidence from contamination, creating the crime scene diagram and establishing crime scene security.

Locking Down the 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

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. For some crime scenes where there are natural barriers, such as buildings with doorways, it is easy to create a crime scene perimeter defining access. This becomes more complicated in outdoor venues or large indoor public venues, where fencing and barricades may be needed along with tape markers to define the perimeters.

Once the crime scene perimeter has been established and lock down has taken place, it becomes necessary to ensure that no unauthorized persons cross that perimeter. Typically, and ideally, there will only be one controlled access point to the crime scene, and that point will be at the entry point for the path of contamination.

Protecting Evidence from Contamination

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.

As an example, sometimes in cases of serious assaults or even murders, paramedics have been present at the scene treating injured persons. When this treatment is happening, non-suspect related DNA transfer between persons and exhibits can occur. Determining those possibilities is one of the first steps in establishing the level of existing contamination at the time of lock down. 

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.

Crime Scene Security

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:

• Forensic specialists
• Search team members
• Assigned investigators, and/or
• The coroner in the case of a sudden death investigation

To maintain a record of everyone coming and going from the crime scene, a document, known as a “Crime Scene Security Log,” is established, and each authorized person is signed in as they enter and signed out as they depart the scene with a short note stating the reason for their entry. Any unauthorized person who enters or attempts to enter a crime scene should be challenged by the crime scene security officer, and, if that person refuses to leave, they can be arrested, removed from the scene, and charged for obstructing a police officer. The assigned security officer is responsible for creating and maintaining the Crime Security Log, which can take various forms. In short term, small scale investigations, it may only require a single page in the security officer’s note book; however, in a large scale, long term investigation, the log could include volumes of pages under the care of several assigned security officers working in shifts. Whatever the scale or format, the security log records who attended the scene, when they attended, why they were there, and when they left the scene. An example of a crime scene security log is shown in the following example (Gehl and Plecas, 2017).

Creating a Field Sketch and Crime Scene Diagram

According to Gehl and Plecas (2017), the next step is to document the crime scene as either a field sketch or a crime scene diagram. Either of these can be done to illustrate the physical dimensions and notable characteristics of the crime scene.

The difference between the Field Sketch and the Crime Scene Diagram is that the sketch, as implied by the name, is a quick rough depiction of the event. The field sketch, like notes in an investigator’s notebook, serves as a memory aid. The crime scene diagram is a more formal representation of the same information, but is composed to scale using the assistance of the field sketch and measurements. In either of these drawings of the crime scene similar core information will be represented.

• If it is a building, it will show the address of the location, entries, exits, windows, the position of rooms, the position of furniture, and the location of all exhibits relative to the crime.
• In an outdoor crime scene, establishing and documenting the location of the scene becomes more complex. The geographic location of an outdoor scene needs to be established relative to some known geographic location, such as a roadway intersection, a mile-marker, or even by way of fixing of GPS coordinates of latitude and longitude to a permanent fixed object at the crime scene. In some cases, such as a large open field, where no permanent fixed objects are available, it may become necessary to place a fixed object like a steel survey pin to mark a fixed point at the crime scene.
• After the initial diagram features are completed and evidence is collected within the crime scene, each of those exhibits will be shown on the diagram with an exhibit number. That number will be cross referenced to the exhibit log that will be completed by an assigned exhibit custodian as part of the crime scene management team. This process of showing each exhibit as a number eliminates the need to clutter the diagram with written description of each exhibit found. In some cases, where there are many exhibits, writing the description of each exhibit onto the diagram would make it unreadable, cluttered, and confusing.
• In addition to existing features and evidence at the crime scene, the diagram will also show the location of the path of contamination that has been established and the external perimeter of the crime scene.
• As part of accepted protocols, these diagrams are always drawn with an orientation to North at the top of the diagram, and all writing on the diagram is oriented in one direction, namely east to west