01.05 Crime Scene Security, Assessment, And Examination

When a crime occurs, it is important to protect the crime scene to preserve the evidence until it can be recorded and collected. The evidence that is documented at the crime scene is used to picture the series of events leading to the crime. This places a huge responsibility on the officers securing the crime scene in following the correct protocols and processes in crime scene management.   
 In this lesson, you will learn how a crime scene is secured, and how evidence is recorded and collected.

By the end of this lesson, you should be able to answer our essential questions:  

• What are the responsibilities of the responding officer, crime scene technician, and investigator? 

• What are the different types of evidence and what are the guidelines for collecting and preserving different types of evidence?  

• What are the various search patterns used at a crime scene when searching for evidence?

Lesson

Securing the Crime Scene

When a crime occurs, it is important to protect and preserve the crime scene as much as possible so that evidence can be collected without contamination. Securing the crime scene is generally the responsibility of the responding police officer and is maintained throughout the investigation until police release the scene from their custody. While it is important to protect the crime scene from contamination, some circumstances require that the officer enter the crime scene such as:

1. A victim who needs life-saving medical assistance

2. The arrest of a suspect still on-scene

Though these conditions may warrant that the responding officer enters the crime scene and potentially disturb the victim or evidence, an officer must ensure that the scene is safe and cleared for the other personnel arriving on-scene. An officer must also provide medical assistance as needed until paramedics arrive if there are any living victims. If an officer does move a victim or disturb evidence, he or she should make notes of how the victim or item of evidence was found upon arriving at the scene and how it was disturbed. These details can be very important in a case.

A responding officer should also take note of various areas of the crime scene such as:

1. The condition of any windows, doors, and lighting

2. Any signs of activity

3. If any noticeable odors are present (alcohol, chemicals, drug residues, etc.)

4. Basic information of any suspect(s) including physical description, physical and mental condition, any intoxication, and any statements.

5. Basic information about the victim(s) and their condition

Next, the crime scene should be marked by crime scene tape or roping so that a visual barrier of the contained area is obvious to those who may enter the crime scene unknowingly. This not only keeps others out of the scene but helps investigators focus their immediate search for evidence. The responding officer should take any witness statements and make careful notes of any observations or leads and report them to the investigator.

Recording the Crime Scene

Crime scenes must be documented throughout the investigation with photography, videography, and sketches. This documentation is vital to the investigation as well as the court case because it helps those not present at the crime scene, such as jurors, to better understand where the evidence originated. It is also often used to refer back to once the crime scene has been released from police custody and new information or leads are found.

Photographing the Crime Scene

While there are several other methods of recording the crime scene such as videography, sketching, or 3D scanning, photography is perhaps the most common. Photographs capture the crime scene as it is at that moment and are very useful in showing the orientation of the evidence in a crime scene. Crime scene photography takes training and skill to obtain quality photos useful in investigations. When documenting a crime scene by the photograph:

Crime Scene Sketch

Photography has limitations, so sketches of the crime scene are also critical. A crime scene sketch is a simple visual tool that can clearly highlight the orientation and location of evidence without the cluttered appearance that photographs can sometimes impart. Crime scene sketches are one of two types:

Rough Sketch

The first sketch was completed at a crime scene. It is a pencil-drawn outline of the scene and location with markings where the fundamental evidence or objects are located in the crime scene. It is not usually drawn to scale, but distances are marked and indicated on the sketch. This sketch is usually completed after photographs are made, but before any evidence or objects are moved.

Finished or Scale Sketch

The final copy of the sketch is an accurately scaled sketch of the crime scene and its fundamental components and evidence. Scaled sketches use standard units of scale such as ¼ " per 1 foot in a large room. When making a final sketch, North must always be at the top of the page and the scene is then oriented from that point in the sketch. A final sketch scene is always oriented from fixed points or locations such as trees, walls, telephone poles, curbs, or other immovable objects.

Videography of the Crime Scene

While photographs and sketches are extremely valuable, the crime scene is often also documented on video. Videography provides an overview of the crime scene and is almost always used in major cases as additional scene documentation. When documenting a crime scene with video:

Learn about special documentation considerations in crime scenes in the activity below.

Evidence Collecting Techniques 

Grid Search

Evidence is the available body of facts or information indicating whether a belief or proposition is true or valid. When investigating a crime scene, one must not only locate, collect and preserve the evidence but must also recognize the differences in types and characteristics of the evidence. Some evidence may indicate a specific person or source, while other evidence may only indicate a generic grouping of people or items. As a Forensic Scientist, it is important to understand the difference so that proper conclusions are drawn from the available evidence.

Determining the origin of an item of evidence requires a comparison to another item to look for shared characteristics. The item of evidence is compared with a known or control sample called a Zone Search. If the standard reference sample matches the evidence sample, then it can often be concluded that they came from the same source or are made up of the same materials.

Crime Scene Search Patterns

When searching a crime scene, crime scene investigators must have a plan for how to proceed. A search plan assists them in not only ensuring that they cover all of the necessary areas of the crime scene, but it also acts as a guide so that they do not accidentally contaminate an area or trample evidence. Review the interactivity below to find out more about common search patterns. Hover your mouse over the images to learn more.

Common Types of Evidence and Collection Procedures