Section 4.2: Criminal Investigations

Fundamentals of Policing by Adam J. McKee

When you watch movies or TV shows about detectives, they often seem like unstoppable heroes who always catch the bad guys. They’re shown living exciting lives, full of danger and mystery-solving. But is this what real detectives do? Let’s find out.

In reality, being a detective is quite different. First of all, those super detectives who seem to solve every case? That’s not very common. In fact, police only solve about 20% of major crimes. This means that 8 out of 10 times, the case remains unsolved.

Another thing about detectives in movies is that they’re always in the middle of thrilling action. The truth? A lot of their time is spent doing something not so thrilling: paperwork. Yes, paperwork is a big part of a detective’s job.

The Challenge of Solving Crimes

Now, let’s talk about solving crimes. Crime shows often present it as a simple puzzle – finding out who did it. However, in real life, it’s way more complicated.

Imagine a giant puzzle with thousands of pieces. Some pieces are missing, some don’t fit, and some might even belong to a different puzzle. That’s what detectives face in a criminal investigation. They have to deal with loads of information, also known as evidence. This evidence can be tricky. It might not be clear how it’s related to the crime, it might be incomplete, or it might not even be accurate.

Moreover, for evidence to be useful in court, it has to meet certain standards. Detectives can’t just present anything they find. The evidence must be strong enough to prove guilt “beyond a reasonable doubt.” That’s a high bar to meet. Plus, there are strict rules about how evidence is collected and handled.

🔍 Reflect

Think about a crime show you’ve watched. How did the detectives solve the case? Now, considering what you’ve learned about real criminal investigations, what might have been different if it were a real-life scenario?

The Role of Investigators in Solving Crimes

The Crime-Solving Process

When a crime happens, the first to respond is usually a patrol officer. Their initial work can sometimes lead to an arrest right there and then. But what happens when they can’t wrap up the case? That’s where a criminal investigator, or detective, comes in.

The Many Skills of a Good Detective

Detectives are like the Swiss Army knives of the police world. They need to know a lot about many different things. This wide range of knowledge and skills helps them do three main things:

  1. Interviewing Is Key: Talking to victims, witnesses, and suspects is a huge part of a detective’s job. It’s one of their most important tasks to gather information.
  2. Crime Scene Investigation: A detective must know how to properly inspect a crime scene. This is where they gather physical evidence.
  3. Working with Informants: Lastly, good detectives know how to find and keep informants. These are people who give them inside information on crimes.

Research Findings on the Role of Investigators

Interestingly, research by the National Institute of Justice (NIJ) suggests that traditional detective work isn’t always crucial in solving crimes. Many serious crimes just don’t have enough evidence. It turns out, patrol officers often play a bigger role in solving crimes than previously thought. Many arrests happen right at the crime scene, rather than after long investigations.

This has sparked a lot of discussion about improving investigations. In the era of community policing, there’s a focus on making detectives more proactive.

Investigative Units in Police Departments

Police departments vary in size, and so do their investigative units. Small departments might have just one investigator, while huge ones like the NYPD have thousands. The number of detectives usually depends on the population size, the department’s philosophy, its overall size, and the local crime rates.

Detectives often specialize based on the type of crime. There are two main categories: crimes against people and crimes against property. In larger departments, you’ll find even more specific divisions, like auto theft, burglary, homicide, and sex crimes units.

Purpose and Challenges of Investigative Units

The main goal of these units is to identify and arrest criminals, and then help prosecute them by providing evidence. Identifying a suspect is usually the first step. Once they have a suspect, gathering evidence to convict them is the next phase.

Sometimes, investigations are more about making the victims feel heard and improving the community’s view of the police. There are times when the chances of solving a crime are low. In such cases, focusing on crimes that are more likely to be solved can be more effective.

🔍 Reflect

Think about a time you heard about a crime being solved. Based on what you now know about the roles of patrol officers and detectives, who do you think played a more significant role in solving that crime, and why?

The Crucial Role of First Responders

When someone dials 911 to report a crime, it kick-starts a crucial process. The first step? A patrol officer is sent to the scene. These officers are often the first faces of law enforcement that people interact with in most criminal cases. The role they play is extremely important.

Preliminary Investigation: More Than Just the First Step

Before detectives get involved, the responding patrol officer does some initial investigating. This is known as a preliminary investigation. In smaller departments, where there might be few or no criminal investigators, this initial step might be the entire investigation. The patrol officer handles everything. That’s why all police officers need to know the basics of investigating, understand criminal law, civil liberties, and the rules about evidence.

The First Tasks in a Criminal Investigation

  1. Figuring Out What Happened: The officer’s first job is to work out the events that occurred. This means finding and talking to anyone who saw what happened – the witnesses.
  2. Deciding the Next Steps: Based on department policies, the officer decides how to proceed. Sometimes, they might conclude no crime was committed, so no further investigation is needed. Other times, if the crime seems minor and can be resolved quickly, they might make an arrest after just interviewing those involved.
  3. Handling Serious Crimes: For more serious offenses, it’s usually mandatory to call in a criminal investigator. But until they arrive, securing the crime scene and protecting any evidence is critical. Evidence must be kept safe and untouched. If there’s even a chance it was tampered with, a court might not allow it to be used in a trial.

The Impact of Successful First Response

When these initial steps are done right, it’s a big win. The crime can be considered solved. But that’s not all. Recovering stolen items, discouraging people from committing crimes, and helping crime victims feel heard are also important outcomes of effective first response.

🔍 Reflect

Think about a time when you saw police officers responding to an incident. How do you think their initial actions impacted the overall investigation of the case?

The Follow-Up Investigation

Transition from Preliminary to Follow-Up Investigation

Once the initial groundwork is laid by patrol officers, and if they can’t solve the case right away, detectives take over. This next phase is known as the follow-up investigation. Here, the detectives’ main mission is to gather enough legal evidence to pinpoint a suspect, make an arrest, and secure a conviction in court. But their job doesn’t stop there.

Beyond Finding Evidence: Other Critical Tasks

  1. Recovering Stolen Property: Getting back what was taken is always a priority.
  2. Assisting the Prosecution: Detectives also help the legal team prepare and present the case in court.

The Importance of Communication Skills

To be a top-notch criminal investigator, you need more than just a keen eye for clues. Excellent communication skills are crucial. This means being really good at conducting interviews and interrogations. These are the skills that help investigators get to the truth and build strong cases.

The Four Pillars of Criminal Investigations

When we talk about criminal investigations, we’re talking about a process that has four main goals:

  1. Confirming a Crime Occurred: First, investigators need to establish that a crime actually took place.
  2. Identifying the Culprit: The next step is figuring out who is responsible.
  3. Apprehending the Perpetrator: After identifying the culprit, they need to be caught and brought to justice.
  4. Gathering Court-Worthy Evidence: Finally, the evidence must be strong enough to support a conviction in court.

These goals guide detectives as they work through the complex puzzle of solving a crime.

🔍 Reflect

Imagine you’re a detective working on a case that’s moved to the follow-up investigation phase. What steps would you prioritize to ensure the case moves toward a successful prosecution?

Physical Evidence in Crime Investigation

Understanding Physical Evidence

Physical evidence is anything you can touch that’s connected to a crime. It’s the real, tangible stuff like fingerprints, blood, fibers, and tools used in the crime, like weapons or burglary tools (like a crowbar). You might also hear it called forensic evidence or scientific evidence. That’s because it needs scientific analysis and interpretation to be helpful in solving a crime.

Two Key Functions of Physical Evidence

  1. Establishing Crime Elements: Physical evidence helps prove that a crime happened. For instance, pry marks on a window can indicate a burglary occurred.
  2. Linking People and Places: It’s also vital for connecting victims to crime scenes, offenders to crime scenes, and various elements of the crime to each other.

A Real-Life Example

Let’s look at a homicide case. A young woman’s body was found on a rural road, strangled with a black electrical cord. There is physical evidence. Investigators found an abandoned farmhouse nearby with a similar electrical cord and tire impressions. This evidence suggested the murder might have occurred in the farmhouse and linked the suspect’s vehicle to the scene.

Establishing Linkages with Forensic Evidence

Most of the time, forensic evidence is used to create linkages. It’s important to remember, though, that physical evidence usually isn’t enough on its own to identify a culprit if they’re not already known. It’s more about proving guilt once a suspect is identified. But there are exceptions, like using fingerprint databases (AFIS) and DNA banks.

With AFIS, fingerprints from a crime scene are compared against thousands in a database. The system can find close matches, potentially leading to a suspect. DNA works similarly, where samples from a crime scene can be matched with profiles in a DNA bank.

🔍 Reflect

Consider a crime drama you’ve seen where physical evidence played a crucial role. How realistic do you think the portrayal of using physical evidence to solve the crime was, compared to what you now understand about its actual use in investigations?

Testimonial Evidence in Criminal Investigations

The Role of Witnesses and Suspects

In criminal cases, apart from physical evidence, people — witnesses and suspects — are key sources of information. Let’s break down what this means:

Types of Witnesses

  1. Primary Witnesses: These are people who saw or heard the crime happen. They have direct knowledge. This includes victims who observed the crime and eyewitnesses.
  2. Secondary Witnesses: They know about events related to the crime but didn’t see it happen. This group includes informants (or street sources) and victims who didn’t actually see the crime.

The Power and Problem of Eyewitness Accounts

Eyewitness descriptions and identifications can be crucial for the police, prosecutors, judges, and juries. But there’s a catch: these accounts are often inaccurate. Many factors, like environmental conditions, the witness’s emotional state, and their expectations, can skew what they remember and report.

Interrogating Suspects: A Different Approach

Interrogating suspects is more about confirming what investigators already suspect than getting new information. The goal is often to get a confession. But it’s tricky because suspects have a strong reason to lie.

Tools to Detect Deception

  1. Kinesic Behavior: This is about reading body language. While not used in court, understanding body movements and posture can give clues about whether someone is lying. The idea is that lying causes stress, and people show this stress physically.
  2. Verbal Behavior: The way a suspect talks can also hint at deceit. Liars might give vague answers, mumble, offer explanations too early, focus on irrelevant but true details, or have selective memory issues.

It’s important to remember that interpreting nonverbal and verbal signs of lying must consider individual, gender, and cultural differences.

🔍 Reflect

Think about a situation where someone told you something that wasn’t true. Did you notice any changes in their body language or the way they spoke? How do you think these observations can be applied in criminal investigations to distinguish between truth and deception?


In the world of criminal investigations, the reality often differs from the dramatized portrayals seen in movies and TV shows. Detectives, contrary to being portrayed as always solving cases, actually solve about 20% of major crimes (USA Facts, 2023). Their work involves a significant amount of paperwork, debunking the myth of constant thrilling action. Investigations are complex puzzles involving various types of evidence, requiring detectives to adhere to stringent standards and procedures for evidence to be court-admissible.

Patrol Officers

Patrol officers often play a pivotal role in solving crimes, sometimes leading to immediate arrests. The initial steps taken by these first responders are crucial in determining the course of an investigation. Small police departments may rely entirely on patrol officers for investigations, highlighting the need for all officers to be well-versed in basic investigative techniques and legal principles.


Detectives are tasked with follow-up investigations when patrol officers cannot resolve a case. Their goal is to collect sufficient legally obtained evidence to identify and arrest a suspect, and aid in securing a conviction. Effective communication skills, particularly in interviewing and interrogation, are essential for detectives. The ability to discern truth from deception through understanding nonverbal and verbal cues is a valuable skill, though interpretations must consider individual, gender, and cultural differences.

Types of Evidence

Physical evidence plays a crucial role in establishing the elements of a crime and linking various aspects of it. However, it usually requires additional information to identify a suspect. Technologies like AFIS and DNA databases aid in this process, providing potential matches that can lead to suspects.

Testimonial evidence from witnesses and suspects is another major information source. Eyewitness accounts, while influential, are often unreliable due to various influencing factors. Detectives must balance the need for accurate information with the understanding that witnesses and suspects may provide inaccurate or deceptive information.

These insights into criminal investigations reveal a multifaceted and challenging process, quite distinct from popular media representations. The roles of patrol officers, detectives, and the nature of evidence all intertwine to form the intricate tapestry of criminal justice procedures.

Key Terms

References and Further Reading

Modification History

File Created:  08/15/2018

Last Modified:  12/14/2023

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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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