Principles of Effective Investigation and Case Study


A criminal investigation is juxtaposed with a jigsaw puzzle. This is simply because it is only the investigators who have some clues, but they lack a picture of how the pieces can be played together. For an investigation to be complete, the investigators have to go to many places to collect different pieces of evidence which they can piece together to achieve a fixed picture and to form an image of the crime. There are various circumstances where the investigators may lack various pieces that can connect the details of a particular crime (Gilbert, 2010, p. 2). This, therefore, implies that the investigators have to look for several sources that may relate to a crime. These sources may include statements from the victims, witnesses, suspects, document archives, and visits to the crime scene. Of these sources of information on crime, some may be willing to provide the information, others may fail to whereas others may not be aware that they hold important pieces of information to a particular criminal investigation and there are also some circumstances where the pieces of evidence to a crime may not be found. Obtaining criminal investigation information relating to a particular crime assists the investigators to obtain important pieces of evidence which when placed together may corroborate or disapprove of a crime (Charles, Neil, Leonard & Robert, 2009, p. 41).

The word investigation has been clouded by predetermined mindset perception. Some people consider it as an art while others treat it as a theory; these are just mere thoughts. The investigation is a scientific exercise since it requires the understanding and knowledge of forensic science. Having forensic knowledge is necessary for an investigation to be successful. Investigations may be concluded at the scene or in the event of an immediate commission of a crime but when it comes to trial; the investigative evidence should be corroborated by forensic evidence (Becker, 2010, p. 1).

The Criminal Investigator

An investigator is understood as an individual who collects, documents, and evaluates evidence and information. The act of performing these activities is referred to as an investigation. A criminal investigation is defined as the collection of information and evidence for identification, apprehension, and the conviction of suspected criminal offenders (Osterburg, 2010, p. 5). The primary objective of criminal investigation and forensic science is to unravel the truth. It is this search for truth that compels investigators to uphold their oath of office and to uphold high moral and ethical standards in the course of executing their duties (Charles, Neil, Leonard & Robert, 2011, p. 2). The main objectives of the investigation are:

  • To establish whether a crime was actually committed or not,
  • To identify the criminal suspects or to exonerate a suspect,
  • To facilitate recovery of stolen property and
  • To aid in the prosecution of individuals who are charged with a crime.

There are some situations where investigators are called upon to testify as witnesses in a court of law, an effective investigator can only provide clear and coherent testimony if he/she has undertaken a credible and comprehensive investigation.

Skills and Qualities of an Investigator

To achieve the above objectives, the investigator should have special knowledge and skills. The most critical skill of an investigator is to be in a better position to converse fluently and equally with people of diverse backgrounds, from an executive person to a cobbler and a prostitute. This is necessary because a most criminal investigation is obtained from people. A competent investigator should distinguish between knowing things and doing things. However, the duties and responsibilities of a criminal investigator have undergone some metamorphosis in recent times; this is due to technological advancements, the emergence of powerful media, and new forms of law. This calls for the investigators to be extremely knowledgeable in a wide range of areas and should be adequately educated and trained particularly concerning complex systems, communication, and writing skills, and social differences. Consequently, some requisite skills and abilities are required of a prosecutor. These include:

Ability to undertake a proper crime scene analysis to establish physical evidence: In this event, the investigator should be well equipped with the skills on how to recognize, collect and preserve physical evidence, i.e. the investigator should be familiar with modern methods and techniques of collecting and recording information (Newburn, Williamson & Wright, 2007, p. 62).

He should also have the ability to question parties to a crime; these may include witnesses and suspects. The skills related to this ability include perfect interviewing and interrogation techniques, knowledge of foreign lathe gauge and street jargon as well as being sensitive about constitutional and civil rights of all individuals.

Ability to write a report: the investigator should have a deeper understanding of how to write a report. He/she should be well versed in a variety of languages.

An effective investigator should be an individual with a lot of skills. Investigators should be people who are emotionally stable, driven by self-motivation, and are physically fit. They should be people who have an understanding of human psychology so as to understand a criminal mind and a criminal motivation. Among the skills that are required of a criminal investigator are:

Rational thinking: this calls for knowledge on deductive and inductive reasoning. The investigator should be able to connect and relate various forms of unrelated facts. They should let facts decide the hypothesis and the theory of the crime in contrast to feeding facts to an already existing theory. Inductive reasoning involves moving from specific details to a general perspective. It involves utilizing economical but factual information to arrive at consistent explanations.

Critical thinking: the investigators should be somebody who sees and not only looks. They should pave a way for critical thinking to dictate the direction of the flowing facts while they are gathered, and the theory synthesized.

Ethics and integrity: the investigator should be somebody with honor and unmatched integrity and with a high moral philosophy to diligently perform his duty without confusion or influence.

Good communication and language skills: the majority of the work of the investigator involves an application of communication and language skills, particularly in the case of interviews and court testimonies (Becker, 2010, p. 13).

Intellectual capacity: there is a lot of training that is required of investigators to enable them to perform their tasks effectively and efficiently. Investigators should have knowledge of the elements of crime and how to apply investigative techniques. Though exceptional intelligence is not a primary requirement for effective investigators, they should have objectivity logic, and common sense. The ability to get and retain information requires a lot of reasoning, which may at times be unskilled (Hess, 2007, p. 9).

Nature of Investigations

There are two main kinds of investigation namely: complain-driven investigation and intelligence-driven information. The former kind of investigation is considered to be reactive, and it may be triggered by an individual or an organization that brings to the attention of law enforcement agencies a crime that has been perpetrated. These individuals may include the victims of that particular crime, witnesses, informants, or the perpetrators of the crime. The most prevalent form of complain driven investigation is property crime. The latter kind of investigation is proactive and only requires the investigators to establish the elements of the crime themselves. This nature of crimes may be victimless or rather covert, and it may include such crimes as terrorism, drugs, gangs, organized crime, and foreign counterintelligence investigation. This form of investigation targets cooperating witnesses, informants, or the assets of the perpetrators to obtain intelligence that may be necessary to conduct an investigation (Harfield & Harfield, 2005, p. 34).

Elements of a Crime

The main objective of an investigator is to establish the truth. This, therefore, makes it imperative for the investigator to allow facts to reign in the course of the investigation while he/she remains neutral. If the facts may not be supportive enough to sustain the investigation or to support the allegations, then the investigator is compelled to terminate the case. If it happens that the facts, information, and intelligence can be pieced together to corroborate the case, then the investigator can put the case forward for prosecution.

Investigation Plan

An investigation plan is drafted after the investigator has comprehended the kind of investigation, whether a complaint or intelligence-based investigation and when he/she is convinced by the details and the elements of the alleged crime. The investigation plan contains among other details, the direction of the case, the investigative techniques to be applied, and the requisite resources that may be required to accomplish and prosecute that particular investigation. The direction of the case concerns the analysis of the goals and the tasks that are material to the investigation; these objectives may be varied during the course of the investigation when fresh facts are unraveled. It is the direction of the case that will determine the necessary logical techniques that may be applied in the case. It is the logical techniques of an investigation that can trigger the required procedures and necessary protocols.

A successful investigation demands a lot of resources. The availability of human resources, compensation material, and necessary tools and equipment are considered instrumental to the investigative plan since they will facilitate the accomplishment of investigation techniques. Investigators are limited by money and human resources hence leading to a shoddy investigation. Due to this, it is imperative for an investigator to demonstrate his understanding of the following facts: kind of investigation, the crime elements, and the creation of a well thought out investigative plan; a better understanding of this will facilitate a launch of thorough investigation (Lushbaugh & Weston, 2011, p. 12).

It is the duty of the investigator to present well-formulated facts that will lead to the prosecution of the case. The investigation facts should be well articulated in a manner to convince the prosecutor that the case is compelling to sustain itself through the prosecution stage. It is always the prosecutors who determine whether or not a case or particular crime should be prosecuted. This principle, therefore, compels investigators to collaborate with the prosecutor from the onset of the investigation so as to instill a sense of ownership into the prosecutor regarding the case. The prosecutor is a shareholder in an investigation since it is the prosecution that verifies any weakness in the case (Hess & Orthman, 2009, p. 32).

Sources of Information in an Investigation

Information can be obtained from a documentary or a human being. The documentary sources include electronic sources like criminal DMV histories, financial documents, and pat case files or court files. Consequently, the human source is instrumental in an investigation, and it is considered the most powerful source that is available to investigators. The human nature of investigation may be categorized as informants, assets, and cooperative witnesses. Information from human sources is treated as background information or first hand and all are valuable. What is critical in analyzing the human source of information for criminal investigation is its reliability or else such information may be treated as questionable and suspected, particularly when it is analyzed before the court. The investigator must ask the individual source questions so as enable him/her to determine the reliability of such information. It is also requisite for the investigator to apply motive as a measure to the reliability of the information. This is because some individuals may be more than willing to provide information for several reasons. There are some instances where individuals may cooperate and volunteer to provide information to achieve monetary gains and also to conspire with the prosecutor (Lyman, 2002, p. 19).

Challenges facing investigators

The three main challenges to the investigator concerning accountability and temptation are drug evidence, money, and the informants. This, therefore, requires that human sources should be handled carefully to enhance and preserve the character of the investigator and to protect the integrity of the investigation. A credible investigation should have both control investigator and alternate investigator, and each should be assigned to a different human source. These two investigators have the duty to create the source and to control their contacts. This is necessary to maintain the confidentiality of the human source and protect the integrity of the investigation. This arrangement can foster a good acquaintance and cooperation between the two parties (Tong, Bryant, & Horvath, 2009, p. 22).

Criminal Intelligence

This is obtained from different sources, and it provides momentum to the direction of the investigation. This particularly applies to the case where there is no authenticity of the suspect or in a situation where there are certain leading indicators that relate to a particular individual but there is no tangible evidence to corroborate the indicators. Criminal Intelligence information is achieved through having a conversation with several people who may be witnesses, victims, suspects and also through perusing court documents, records of criminal histories, and analyzing background information. It is the duty of the investigator to therefore weigh the probative value of all criminal intelligence against other intelligence pieces that form the case. There are some circumstances where criminal intelligence may be non-sensual until an investigation is carried out exhaustively (Vecchi, 2009, p. 4).

Investigators utilize various protocols when they are structuring their investigations. There have several steps that should be followed for an investigation to be complete. This is understood as follows.

Types of evidence

In a criminal investigation, there are four types of evidence: physical evidence, circumstantial evidence, forensic evidence, and testimonial, evidence. Physical evidence enables the investigator to prove the guilt or innocence of a person, particularly in the court of law. An individual may be convicted only with the presence of physical evidence, but it may not be enough to prosecute an individual based only on testimonial evidence. Physical evidence can be direct or circumstantial. Direct evidence stands on its own and is instrumental in proofing facts about a particular criminal investigation. Circumstantial evidence, on the other hand, proves facts indirectly. Virtually, all forensic crime investigation is regarded as important. Physical evidence is instrumental in determining whether the evidence is linked to the suspect. Physical evidence may include tool marks, laundry marks, which may be found or often left on the crime scene. The veracity of physical evidence is determined and applied based on its originality (Becker, 2010, p. 2). Forensic evidence has gained prominence in modern times, mainly due to scientific advancement and the changing nature of the legal system. Due to the principle of protection against self-incrimination and right to counsel in the time of interrogation of the suspects who are legal matters, the investigators have found it necessary to attach little importance to confessions and to rely heavily on forensic evidence in order to achieve convictions (Becker, 2010, p. 6).


A successful investigation should utilize the principle of parsimony. This implies that the investigator should find a simple description of the matter being examined. An investigation should begin to form the simple details and end with complex details of the crime (Stelfox, 2009, p. 7).


An effective investigation should be specific. The plan should be vivid as to what exactly is to be investigated and how is it going to be investigated. This is necessary to determine the techniques that are to be applied and to have a clear picture of the intended outcome.

Preservation of the Crime Scene

Once the investigator arrives at the crime scene, he should ensure that the scene is protected and preserved. If there are still victims at the scene, then they should be immediately helped or moved out of the crime scene. It is also necessary to determine the boundaries of the scene before securing it, protection of the crime scene is necessary because physical evidence is often obtained from the scene. Upon securing the scene, the investigator should not haphazardly work around the scene for fear of tempering with impression evidence. At the crime scene, the investigator should ensure that all the victims, witnesses, or suspects are kept away from each other until they are interviewed. They should be informed not to provide information to anybody (Vecchi, 2009, p. 5).

Processing and Collecting Evidence

There are various rules that investigators should carefully follow when collecting criminal evidence, these are:

  1. The investigator should give priority to all fragile evidence that can be susceptible to alterations.
  2. Items that can hinder an effective investigation should be removed.
  3. The evidence should have investigators’ initials and the date and time when the evidence was collected on the container of the evidence.
  4. The investigator should examine, take a photograph, sketch, and collect the evidence in a way that is coherent, consistent, and logical.
  5. The prints of the investigators and other people who can access the crime scene should be eliminated.

Forensic Science

Forensic science is considered the best alternative to other sources of crime information; two categories of forensic science are criminalist and forensic medicine. Forensic science involves the carrying out of recording and scientific examination of physical evidence in a criminal investigation. According to the American Academy of Forensic Science, forensic science investigation is the use of science for the purposes of fulfilling the demands of the law; forensic science involves the evaluation and examination of fingerprints, firearms, tool marks, and any other document in question (Nickell & Fischer, 1999, p. 3). Forensic investigation is aimed at: identifying the object or instrument of crime, establishing the nexus between the available physical evidence, the victim of the crime, the suspect, and the crime scene, to offer testimony in a court and be able to reconstruct how a particular crime was committed (Osterburg, 2010, p. 22). The forensic investigation involves the collection of facts about a particular criminal activity that may be used for evidence in a court of law. It is the scientific identification of the witnesses, the exhibits, and the suspected offenders. Forensic investigation has been favored and trusted by investigators because the traditional methods of investigation are unable to cope with intensifying complexities of crime like financial fraud, theft syndicate, and corruption. Just like a criminal investigation, forensic investigation is instrumental in probing the truth and ascertaining facts about a particular crime.

Case study: Investigation into the Assassination of JF Kennedy

Immediately a crime is committed, the first principle of investigation is to rush to the valuate an evaluation to obtain clues. Once this is complete, the investigators can move to the next phase which involves focusing on individuals who may have committed the crime. This can be verified by looking at any nexus between the evidence at hand and the suspects. This can be achieved through logical deduction or rather common sense. Deduction in criminal investigation demands that the suspect be examined based on three aspects of crime, namely: character, motive, and opportunity. This will lead to separation of the suspects according to the two categories, the prime suspect and the suspect. With the emergence of new form of evidence, the additional form of logical deduction, the suspects get to be moved from one category to another, and it might end in the identification of one prime suspect who may be a probable culprit who can ultimately be charged for having committed the crime (Zirbel, 1991, p. 95).

In the case of President JF Kennedy assassination, the Warren commission which was tasked to investigate into the circumstance of the assassination; the commission only undertook an investigation to one of the prime suspects called Lee Harvey Oswald. The commission failed to examine any criminal potential of other probable suspects. Varied opinions concluded that by only concentrating their investigation on only one suspect, the commission failed in its duty to undertake a comprehensive investigation of the President’s death. Subsequent investigations corrected this error by performing their criminal investigations on other suspects like mafia, ultra conservatives and communists. The latest criminal investigation into the assassination of the president is the investigation of Lyndon B. Johnson, who was the resident right-hand man. This was undertaken by investigating his character traits, which may provide disposition to his ability to commit a crime. His character and motive were also evaluated (Zirbel, 1991, p. 96).

Character Evidence in JF Kennedy Assassination Investigation

Character disposition is applied in analyzing individuals’ chances of committing a crime, and it makes explicit the character of an individual and their usual action in certain situations. Though character disposition may not conclusively establish that an individual has committed a crime, it can be instrumental in determining the likelihood that he might have committed a crime. Individual moral conduct will aid the investigators to evaluate the suspect’s attitude based on his conformity to rules of morality and with regards to his conduct.


The degree of success of an investigation depends on the expertise and resources availability in the side of the investigator, and the extent of freedom guaranteed to the investigator by the security agencies. Furthermore, the source of the information and the criminal intelligence that is adduced are fundamental principles to an effective and successful investigation. It is imperative upon the investigators to develop a better understanding of how to access, verify, ascertain and to handle source information that is necessary for the accuracy of the criminal intelligence or that can facilitate further investigations. The handling, processing and preservation of the evidence can directly affect its value, and it is important for the investigator to have a vivid understanding of how to secure and obtain evidence particular in the crime scene.


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LawBirdie. "Principles of Effective Investigation and Case Study." March 27, 2023.