Crime scene searches and evidence collection are the backbone of criminal investigation. If the crime scene boundaries are not adequately identified, with an appropriate search and systematic identification and collection of evidence to follow, then cases may not be prosecutable.
Crime scenes are sources of evidence, and therefore must be painstakingly examined for both visible and latent evidence. Searches may vary by type of crime, geography, human resources, and availability of equipment. Of particular note is that the size of an organization, which directly affects human resources, dictates who conducts a crime scene search and collects evidence. In small organizations, which represent approximately 90% of local police agencies, it is common for one officer to be responsible for not only responding to a crime scene, identifying and searching the scene, but also for identifying and collecting the evidence. In medium and large organizations, however, where there tends to be more specialization among duties, one or more officers might be responsible for each of the preceding tasks.
Purpose of a Crime Scene Search
The primary purpose of a crime scene search is to develop associative evidence that could link a suspect to the scene or a victim, and to answer questions crucial to the investigation, such as who perpetrated the crime, how the crime was committed, the circumstances surrounding the commission of the crime, and why the crime was committed. Additionally, police search crime scenes to identify evidence through which a psychological profile of the suspect can be developed, to identify an object(s) that does not logically belong at the crime scene and that could potentially be linked to a suspect, and to identify the suspect’s modus operandi (MO), or motive for committing the crime (Oster-burg and Ward 2004; Swanson, Chamelin, and Territo 2003). It is important to note that although these principles apply to all crime scenes, more specific tasks may be undertaken, depending on what type of crime has been committed.
Swanson, Chamelin, and Territo (2003, 51-55) indicate that there are five primary considerations for conducting a crime scene search: (1) boundary determination, (2) choice of search pattern, (3) instruction of personnel, (4) coordination of efforts, and (5) processing of the evidence. Again, it should be noted that depending on human resources available, one officer or a number of officers might be responsible for these tasks.
Determining the boundary of the crime scene is critical. Numerous factors affect boundary determination, such as whether the crime scene has more than one location, and whether the crime scene is indoor or outdoor. Crime scenes may be categorized into primary and secondary, though secondary crime scenes do not always exist when the crime occurred in only one area. Typically when a crime scene is inside a physical structure (indoors), boundaries are restricted and more easily identifiable. In contrast, with an outdoor crime scene, determining accurate boundaries is more challenging.
Additionally, crime scenes are divided into inner and outer perimeters, with the inner perimeter being where the actual crime took place and the outer perimeter being the boundary for maintaining control of the crime scene (Swanson, Chame-lin, and Territo 2003).
Choosing a search pattern is critical and depends on the locale, size of the area, and the apparent actions of the suspect, victim, and any others having access to the scene, that is, witnesses (Saferstein 2004). The number of personnel available also affects the type of search, with some methods requiring more personnel than others.
Types of Crime Scene Searches
Common search patterns include the spiral, strip/line, grid, zone/quadrant, and pie/ wheel. The spiral search is used most often for outdoor crime scenes, is conducted by one person, and is done by walking in a circle from the outermost point of the inner perimeter toward the center of the circle. The strip/line search is done by dividing the crime scene into a series of lanes in which personnel search up and down the lanes until the scene is completely searched. A grid search is similar to a strip/line search but is also divided into lanes perpendicularly, thereby constituting a more systematically thorough search from multiple perspectives. A zone/quadrant search is one in which the crime scene is divided into four quadrants and searched using another method, such as a strip or line search. In a pie/wheel search, the crime scene is divided into a large circle with numerous sectors, and searched using another method, such as a strip/line search. Practically speaking, a strip/line or grid search is used most often (Swanson, Chamelin, and Territo 2003).
Careful instruction of personnel, when more than one officer is involved, is of the utmost importance. When numerous individuals are involved in searching a crime scene, it is imperative to delineate responsibilities to provide for a thorough, systematic search, but also to ensure that efforts are not duplicated. Additionally, continuous coordination of tasks may provide for effective and efficient completion of searches, regardless of how many people are involved. Comprehensive instruction and coordination of crime scene search efforts result in optimal conditions for the identification and collection of evidence, which can ultimately lead to a successful prosecution.
Evidence Collection
The type of evidence officers look for will typically be determined by the circumstances surrounding the crime. Physical evidence may be visible and easily identified in some cases, and in other cases evidence may be invisible and only detected using advanced technologies. While evidence is typically searched for at a crime scene, evidence may also be found in other places, such as on a suspect or victim, or at a morgue or laboratory. Therefore, it is extremely important to examine less obvious places and/or items that might contain potential evidence, such as a vehicle or a victim’s clothing (Saferstein 2004).
Physical evidence may be collected so that it is not altered from the time it is removed from the scene or other receptacle, until it is transferred to the crime laboratory. However, changes in the state of the evidence may occur due to contamination, breakage, evaporation, scratching, bending, or improper packaging. Also critical to the evidence collection process is the proper packaging of evidence, which means that each item must be collected and placed in a separate container to prevent damage and maintain the integrity of the evidence (Saferstein 2004).
Although digital evidence is a form of physical evidence and is commonplace in many crime scenes today, the identification and collection of digital evidence presents unique challenges for law enforcement. Digital evidence, or electronic evidence, is ”any data stored or transmitted using a computer that support or refute a theory of how an offense occurred or that address critical elements of the offense such as intent or alibi” (adapted from Chisum 1999, as cited in Casey 2004). Digital data is the binary numerical representation of information such as text, images, audio, or video. Digital evidence is typically the product of crimes such as fraud, child pornography, and computer intrusions.
Even though digital evidence is prevalent today, many police organizations have limited capabilities when it comes to not only handling, but simply identifying digital evidence. Particular challenges regarding digital evidence include but are not limited to these: (1) Digital evidence is difficult to handle, (2) digital evidence represents only an abstraction or part of what occurred during the criminal activity, and (3) digital evidence is easily manipulated (Casey 2004). With technology advancements occurring every day, it is likely that handling digital evidence will increasingly become a major part of crime scenes in the future.
Another important consideration when collecting evidence and subsequently transferring it to the crime laboratory is chain of custody, which means ”continuity of possession” (Saferstein 2004, 45). Practically speaking what this means is that all personnel who have handled the evidence must have maintained its integrity and provided no means through which the evidence could have been altered. When evidence is finally presented in court, if the chain of custody cannot be established, then the evidence will probably not be allowed to support the prosecution’s case.
Following identification and collection, evidence is submitted to a crime laboratory for analysis. Transferring of the evidence may take place by personnel delivering the evidence themselves or, in some cases, transferring may occur by mail or other means of shipment. Regardless of the method of transferring the evidence to the crime laboratory, the chain of custody must be maintained throughout the process.
Crime scene searches and evidence collection constitute a vital part of the duties of law enforcement. Strict adherence to policy and procedure, as well as thoughtfulness and common sense, contribute significantly to not only a successful prosecution, but also to the effectiveness and efficiency of police operations.
