Policing | Section 4.2

Fundamentals of Policing by Adam J. McKee

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Criminal Investigations

Hollywood is responsible for several archetypical “investigators.”  Most of these are merely Hollywood myths that reflect nothing of what criminal investigators actually do.  Perhaps the most unrealistic myth is the super sleuth that “always gets his man.” In reality, police clear only about 20% of index crimes.  The next most unrealistic myth is that detectives live a professional life of danger and excitement. The reality is that detectives do a huge amount of boring paperwork.

The crime fiction model of “who done it” paints an oversimplified picture of the criminal investigation process.  A major problem for the police in conducting a criminal investigation is that not only is there potentially massive amounts of information (evidence) available, but the relevance of the information is often unknown, the information is often incomplete, and the information is often inaccurate. Further, to be useful in proving guilt in court (where beyond a reasonable doubt is the standard), the evidence must have certain other qualities, and certain rules and procedures must be followed in collecting the evidence.

What Investigators Do

Many crimes that result in arrest do so because of the “detective work” of the patrol officer that responded to the call for service.  If the patrol officer cannot conclude the investigation with an arrest, the case is turned over to a criminal investigator. The primary job of the investigator is to gather information.  A good detective is a jack of all trades. Much knowledge about a wide array of subjects and many skills are required. These are needed to accomplish three major functions: Conducting interviews of victims, witnesses, and suspects is perhaps the most common and most important.  Second, a good investigator must have the necessary knowledge and skill to properly conduct a crime scene investigation. Finally, good detectives must have the ability to develop and maintain informants.

The research suggests that the traditional investigator’s role is not that important in solving crimes.  According to the National Institute of Justice (NIJ), no amount of investigation will solve many of the serious crimes that occur in America’s communities.  There simply is not enough evidence to go on. Other studies have found that the majority of cleared cases are cleared because of the work of patrol officers.  The arrest of offenders at the scene is more common than offenders being apprehended after lengthy investigations. These findings have led to much discussion on how to improve investigations.  As one would expect in an era of community policing, much of that discussion has been centered on how to make detectives a more proactive part of the police department.

Most police departments of any size have a full-time investigative unit.  Very small departments may only have one investigator, while very large departments (e.g., NYPD) will have thousands.  The biggest factor in determining the number of detectives is (of course) the population of the area that the department serves.  Other important factors include the policing philosophy of the department, the size of the department, and crime rates within the department’s jurisdiction.  Investigative tasks are most often divided among officers according to the type of crime committed. The most general divisions are crimes against persons and crimes against property.  The larger the department, the more subdivision that will be found in investigative unit specializations. For example, property crime can be subdivided into investigative specialization in auto theft, burglary, and larceny.  Crimes against persons can be divided into homicide, sex crimes, robbery, and assault.

The major purpose of investigative units is to identify, arrest, and provide the prosecution with evidence against criminal offenders.  In the initial phases of a criminal investigation, the top priority will usually be to identify a suspect. The majority of times, the apprehension of a criminal suspect is a matter of standard operating procedure once a suspect has been identified.  Once the offender has been identified, the next phase is usually to seek evidence to help convict the offender. Often, criminal investigations are conducted to placate the victim and create a positive attitude toward the police among community members.  Many times, law enforcement are well aware that the probability of resolving a particular crime is very low. In these cases, the goal of resolving crimes and arresting offenders would be better served by focusing on cases with a high probability of resolution.

The First Responder Role

The vast majority of criminal cases begin with a call to 911.  Such calls will usually result in a patrol officer being dispatched to the scene.  This means that patrol officers answering calls are the first representatives of law enforcement to deal with most cases.  The importance of this role should not be underestimated. Before a case is turned over to criminal investigators, the responding patrol officer will usually conduct a preliminary investigation.   Often, when departments are small and there are few or no criminal investigators, the preliminary investigation will become the full investigation and the responding officer will conduct all investigative tasks.  This fact speaks to the need for all police officers to be well versed in basic investigative techniques as well as the legal foundations of criminal law, civil liberties, and evidence law.

The first task of an officer conducting a criminal investigation is to determine what actually happened.  A key element in determining what happened is to locate and identify all witnesses. There is also a need to determine what further investigative steps should be taken.  Departmental policy will often guide first responders in making this decision. The first responder may determine that no crime has been committed and that no investigation is warranted.  The officer may determine that the crime is a minor one and that an arrest can be made with no further investigative tasks beyond interviewing witnesses victims, and suspects.

If the crime is a serious one, most departments require that a criminal investigator be notified.  The initial security of the scene and the protection of evidence is a key responsibility of the first responder.  To be admissible in court, no opportunity can exist for evidence to be damaged or tampered with. If such an opportunity is even a possibility, a judge may later determine that any evidence found at the crime scene is inadmissible.  If the first three objectives are successfully attained, then the crime can be said to be solved. Several other outcomes such as recovering stolen property, deterring individuals from engaging in criminal behaviors, and satisfying crime victims have also been associated with the process.

The Follow Up Investigation

Upon completion of the preliminary investigation (and the first responder cannot resolve the case), the case will usually be turned over to investigators.  The phase of the investigative process undertaken by these investigators is usually called the follow-up investigation.  The driving goal of detectives conducting a follow-up investigation is to identify and collect sufficient legally obtained evidence to identify a suspect, make an arrest, and gain a conviction in criminal court.  In addition to obtaining information and evidence, the detectives have other tasks associated with criminal investigations. The recovery of stolen property should be a priority. In addition, detectives are often called upon to assist the prosecution in the preparation and presentation of the case.

Criminal investigators (and by extension all police officers) must have well-developed communication skills.  The art and science of interviews and interrogations must be mastered by an officer seeking to become a successful investigator.  

Goals of Criminal Investigations

criminal investigation refers to the process of collecting evidence about a crime in order to:

      1. determine if a crime has been committed
      2. identify the perpetrator
      3. apprehend the perpetrator; and
      4. provide evidence to support a conviction in court

Physical Evidence

Physical evidence is evidence of a tangible nature relating directly to the crime. Physical evidence includes such items as fingerprints, blood, fibers, and instrumentalities (tools) such as weapons, burglary tools (e.g., a crowbar), and so forth. Physical evidence is sometimes referred to as forensic evidence or scientific evidence, implying that the evidence must be scientifically analyzed and the results interpreted in order to be useful.

Physical evidence can serve at least two important functions in the investigative or judicial process. First, physical evidence can help establish the elements of a crime. For example, pry marks left on a window (physical evidence) may help establish the occurrence of a burglary. Second, physical evidence can associate or link victims to crime scenes, offenders to crime scenes, victims to victims, instruments to crime scenes, offenders to instruments, and so on.

For example, in a homicide case, a body of a young female was found along a rural road. Knotted around her neck was a black electrical cord (physical evidence). The cause of death was determined to be ligature strangulation via the electrical cord. Upon searching the area for evidence, an abandoned farmhouse was located and searched, and a piece of a similar electrical cord was found. This evidence led the investigators to believe that the farmhouse may have been where the murder actually occurred. Further examination of the scene revealed tire impressions from an automobile (more physical evidence). These tire impressions were subsequently linked to the suspect’s vehicle.

Most forensic or physical evidence submitted for analysis is intended to establish associations. These associations are often referred to as linkages.   It is important to note that physical evidence is generally not very effective at identifying a culprit when one is not already known. Typically the identity of the culprit is developed in some other way and then physical evidence is used to help establish proof of guilt. Possible exceptions to this pattern are fingerprints (when analyzed through AFIS or Automated Fingerprint Identification System technology) and DNA banks. With AFIS technology, fingerprints recovered from a crime scene can be compared with thousands of other prints on file in the computer system at the law enforcement agency. Through a computerized matching process, the computer can select fingerprints that are close in characteristics. In this way, a match may be made and a suspect’s name produced.

Testimonial Evidence

Besides physical evidence, another major source of information in a criminal investigation is people, namely witnesses and suspects. Witnesses can be classified as either primary or secondary. Primary witnesses are individuals who have direct knowledge of the crime because they overheard or observed its occurrence. This classification would include crime victims who observed or who were otherwise involved in the offense. Eyewitnesses would also be included here. Secondary witnesses possess information about related events before or after the crime. Informants (or street sources ) and victims who did not observe the crime would be best classified as secondary witnesses.

Besides the basic information about the particulars of the criminal event and possibly the actions of the perpetrator (to establish a modus operandi), another important type of information often provided by witnesses is eyewitness descriptions and identifications. Such information is quite powerful in establishing proof—for the police, prosecutor, judge, and jury—but the problem is that eyewitness identifications are often quite inaccurate and unreliable (Loftus et al.). Research has shown that many factors—such as environmental conditions, physical and emotional conditions of the observer, expectancies of the observer, perceived significance of the event, and knowledge of the item or person being described—can significantly influence the accuracy of eyewitness statements.

In contrast to interviews of witnesses, interrogations of suspects are often more accusatory in nature. Usually, interrogations are more of a process of testing already developed information than of actually developing information. The ultimate objective in an interrogation is to obtain a confession.  

For obvious reasons, offenders have great incentive to deceive investigators. Understanding this, there are several tools available to investigators who wish to separate truthful from deceptive information. First is the understanding of kinesic behavior, the use of body movement and posture to convey meaning (Walters). Although not admissible in court, information derived from an understanding and interpretation of body language can be quite useful in an investigation. The theory behind the study of nonverbal behavior is that lying is stressful and individuals try to cope with this stress through body positioning and movement.

Much like nonverbal behavior, verbal behavior can also provide information about the truthfulness of a suspect. For example, deceptive subjects tend to provide vague and confusing statements, talk very soft or mumble, provide premature explanations, focus on irrelevant (but truthful) points in an explanation, or may claim memory problems or have a selectively good memory. Of course, interpretations of nonverbal and verbal behaviors in terms of deception must consider individual, gender, and cultural differences in personal interaction.


Key Terms

References and Further Reading

“Police: Criminal Investigations.” Encyclopedia of Crime and Justice. Retrieved March 03, 2019 from Encyclopedia.com: https://www.encyclopedia.com/law/legal-and-political-magazines/police-criminal-investigations

Modification History

File Created:  08/15/2018

Last Modified:  06/21/2019

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This work is licensed under an Open Educational Resource-Quality Master Source (OER-QMS) License.

Open Education Resource--Quality Master Source License


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