Follow-Up Investigation

A detective or criminal investigator may be assigned to a case and may even show up at the crime scene before the patrol officer leaves. In our example of a student who is robbed and assaulted, this occurrence may be so common that no investigation takes place beyond the preliminary one. However, if there has been a rash of such crimes in the vicinity of the campus, apprehending the offender or offenders may be a priority and a senior criminal investigator may be assigned to the case and assume responsibility for what happens from that point on.

In order to fulfill his or her responsibility for investigating the crime, he or she may conduct a visual inspection of the crime scene and develop a preliminary plan for the investigation. In addition, the senior investigator will decide what other services or resources are needed. For example, if the suspect was seen entering a nearby apartment building, the investigator may call for personnel to search the apartment building or ask for a search warrant if there is a suspect who has been identified as living in that apartment building.

Among the tasks undertaken or procedures utilized by the senior investigator are interviewing the victim again or interviewing other witnesses, conducting or supervising the neighborhood canvass, interrogating the suspect if he or she is in custody, and searching for and collecting other evidence.


There are three broad categories of evidence that investigators attempt to locate:

  • 1 Corpus delicti: Evidence that will help substantiate the elements of the crime. For instance, the primary corpus delicti evidence in our example of the robbery of a backpack and laptop computer would be the backpack or laptop computer.
  • 2 Associative: Evidence that connects a suspect to the scene or the victim, or connects the scene or victim to the suspect. For example, if a suspect is arrested after using a credit card belonging to the student whose backpack was stolen, the possession and use of the stolen credit card would connect the suspect to the scene and the victim.
  • 3 Tracing: Evidence that helps to identify the offender. For instance, if the victim of our backpack robbery scuffled with the perpetrator and the perpetrator’s wallet was dropped at the scene, the driver’s license in the wallet could lead the police to the residence of the suspect, and that would help to identify the offender.

Direct and Circumstantial Evidence

During a criminal investigation, there are two basic kinds of proof needed to establish the guilt or innocence of a suspect. One type of proof is direct evidence, and the other is circumstantial.

Direct evidence involves testimony by eyewitnesses who have information to offer about the crime through one of their five senses. That is, they have seen, heard, smelled, tasted, or touched something related to the crime and, perhaps, related to the suspect. There are two general categories of witness: those who come forward with the evidence willingly and those who are unwilling—or reluctant—witnesses. Circumstantial evidence, on the other hand, is evidence from which inferences can be drawn and include items such as physical evidence (Weston and Lushbaugh, 2006). Usually, circumstantial evidence includes weapons, blood, fingerprints, tool marks, documents, and dust, dirt, or other traces.

Standard operating procedure is for the first patrol officer at the scene of the crime to detain witnesses and other persons who might offer help. That officer must obtain adequate information about each witness or each person who may have information to contribute. That would mean getting names, addresses, and phone numbers so detectives can follow up. It also means getting a description of the perpetrator from witnesses and securing a more complete description of the facts of the crime. A canvass of the neighborhood or surrounding area may be undertaken by the initial officers on the scene or later by investigators.

Circumstantial evidence may be found at the scene and must be handled in such a way that the evidence is not compromised or contaminated. Any evidence found at the scene should be secured by the patrol officer or investigator.

Basic Investigative Leads and Informants

The biggest challenge in an investigation is when the offender is unknown. If the victim or witnesses can pinpoint a suspect, then the offender is known and the police can make an arrest. Cases involving named suspects are a high percentage of the cases cleared by arrest in any police department (Weston and Lushbaugh, 2006). It is the unknown offender who presents the biggest problem. In these cases, the investigator must develop the basic investigative leads to attempt to discover the identity of the perpetrator.

The basic lead, in many instances, comes from the victim. It is not always so much that a victim knows the offender, but the detective can develop a lead by learning more about the victims activities just before the crime. A detective will want to make a list of those people who would benefit from the crime and who might have known about the victim and what he or she possessed (e.g., that a student walking home from the library would have a laptop computer in her backpack). Information from the patrol officer on the scene initially may result in further intelligence about possible suspects or vehicles in the area. Fingerprints or other evidence at the scene may help confirm that a suspect was at the scene of the crime, and thus had opportunity to carry out the offense.

Another lead may come from the way in which the crime was committed. This is the modus operandi. In our running example in this chapter, if similar robberies were reported involving female students walking home from the library late at night with backpacks or laptop computers, the pattern may suggest a suspect, or information from previous such crimes can be combined to offer leads. Furthermore, recovered stolen property may be traced to the robber. Or photos of persons arrested for similar crimes might be viewed by victims to see if an identification can be made.

Experienced investigators will avoid hunches or developing leads or suspects based on intuition. Instead, they realize that developing leads conies about best when investigators use their know-how, their cognitive processes, and their ability to work a case rapidly (Weston and Lushbaugh, 2006). The latter point is important. Time is of the essence in most criminal investigations because lapsed time diminishes the victim’s or witnesses’ memory, and provides an opportunity for the offender to dispose of the evidence, develop an alibi, or get away if he or she is fleeing the area.

Some leads turn out to be productive; others may be unproductive. But both require manpower and resources. However, there is no way to predict which are the valuable leads that will be useful versus those that will be a waste of resources.

Also, the fact that a suspect is named or identified by a victim or by witnesses does not mean that that person committed the crime or knows anything about it. Victims—and witnesses—can be mistaken, have their facts all wrong, or be attempting to cause trouble for some innocent party' (Swanson et al., 2012). The integrity and ethics of the investigator play' a key role in ruling out suspects when they are innocent, along with ruling in suspects when there is evidence suggesting guilt.

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