By Dr. Matthew Loux and Bryce Loux | 07/29/2025
The criminal investigation process forms the framework of the justice system. It is an orderly approach to gathering information, obtaining evidence, and capturing and prosecuting offenders.
Coordination between law enforcement, forensic specialists, legal authorities, and the public is essential. When conducted properly, investigations preserve the rule of law and due process and aid in providing justice to victims and their families.
The criminal investigation process is not simply about arresting suspected offenders; it is about providing justice. It establishes legal guidelines for bringing law enforcement to a crime scene, collecting evidence, and presenting that evidence in court.
Any mistake can cripple a case, set the guilty party free, or wrongly imprison an innocent person. Failure to adhere to the criminal investigation process could prove to be detrimental, so this process is paramount to every criminal investigation.
Criminal investigators typically navigate a wide array of crimes, ranging from physical assaults to cyberattacks and complicated financial scams. Modern tools like DNA examinations, digital forensics technologies, and surveillance systems have changed the way we solve cases.
Still, human skills, such as the ability to interview witnesses, remain unmatched when it comes to investigative techniques. Solving criminal cases requires active participation from everyone in the criminal justice community, including police officers, investigators, prosecutors, and judges. These public servants all have integral roles throughout the criminal investigation process.
Initial Response and Securing the Crime Scene to Preserve Evidence
The first phase of a crime scene investigation sets a precedent for how the entire case will unfold. Regardless of whether the scene involves a burglary, a homicide, or any other type of crime, police officers must quickly respond.
Upon their arrival, police evaluate the scene and manage competing priorities. Their immediate concerns are always the same:
- Protecting public and personal safety
- Providing emergency assistance to any injured individuals
- Securing the scene
First-arriving officers complete a primary assessment of the environment to search for potential threats. From there, the focus remains on containment and protecting the safety of others.
In cases involving active shooters, for example, first-responding officers need to determine whether the suspects are still at the scene. Police will assess and neutralize active threats so that EMTs can assist victims.
Meanwhile, all first responders must follow scene management protocols. Scene management involves taking precautions to preserve evidence and avoid disturbing the scene. For instance, EMTs strategically position themselves to protect critical information and physical evidence, like victim positioning and blood spatter.
In addition, police must control the scene with physical boundaries to restrict entry to only authorized people. Police tape or patrol cars are commonly used to create boundaries.
First-responding officers also start a log to create a record of everyone who enters and exits the area. This record includes – but is not limited to – the names of officers, detectives, forensic investigators, and other officials.
Launching a Criminal Investigation
Officers start the criminal investigation process by making preliminary assessments. For instance. For instance, they look for:
- Out-of-order items
- Signs of forced entry
- The arrangement of items
- Readily accessible weapons
- Fleeing suspects
These details are crucial when it comes time for prosecutors to present evidence in court.
In criminal investigations, every second counts. There are myriad factors that can destroy trace evidence, such as crowds, weather, or even well-meaning individuals.
For instance, the 1996 JonBenét Ramsey case remains cold, partly because the crime scene’s integrity was compromised. Friends and family inadvertently contaminated physical evidence as they searched for JonBenét.
By the time law enforcement arrived to secure the scene, the damage was already done. This contamination of key evidence became a major focus of public attention and concern.
Preserving the integrity of evidence in any criminal investigation is critical. A compromised scene can lead to incorrect conclusions, neglected opportunities, and an unsuccessful prosecution. Proper evidence protection is not mere protocol, but the foundation of justice.
Crime Scene Documentation and Evidence Collection
Once a scene is secured, investigators start documenting and collecting evidence in an organized, methodical manner. The documentation serves as a record that prosecutors can use in court to reconstruct the scene and explain how investigators collected evidence.
Typically, criminal investigations combine three primary methods of documentation:
- Photographs – Photographs capture the scene and its surrounding areas with wide, medium, and close-up shots of direct evidence, such as bloodstains and weapons.
- Sketches – Sketches provide spatial relationships and measurements, which allow the jury to visualize the layout.
- Written notes – Written notes identify the items and describe their condition and location.
Such documentation is crucial to the chain of custody, a legal record that tracks each handler of a specific piece of evidence. If the chain is broken – e.g., evidence goes missing or is accessed by unauthorized personnel – the evidence may be ruled inadmissible in court. Consequently, breaking the chain of custody could be catastrophic for the prosecution.
Criminal investigators must exercise the utmost care as they collect evidence, which may include:
- Biological materials such as blood, hair, and semen
- Trace evidence including fibers, soil, and gunshot residue
- Ballistics like bullet casings and firearms
- Digital evidence from phones, laptops, and security cameras
Each item must be stored in an appropriate container. For example, paper bags can help inhibit mold growth on biological samples, while anti-static bags help prevent damage to electronics.
Any oversight throughout an investigation can severely impact the outcome of a case. One of the most notorious examples stems from the O.J. Simpson trial in 1995.
Investigators stored blood samples improperly, which resulted in cross-contamination. This lack of proper evidence handling became a focal point for the defense and instilled reasonable doubt in the minds of jurors.
If not for these mistakes, it’s quite possible Simpson would have been found guilty. Each and every clue works together to build a robust hypothesis and support the prosecution’s case.
Interviews and Interrogations
As soon as investigators finish collecting evidence, they begin speaking with witnesses, victims, and suspects. Interviewers need to have a comprehensive grasp of the psychological and emotional conditions of the people they interrogate.
They may apply the cognitive interview technique to help interviewees recall relevant information. Many criminal investigations also employ the Reid Technique®, although concerns about its ethics and tendentious nature have been raised in relation to vulnerable groups.
Some legal restrictions govern the interrogation of suspects. For example, investigators cannot interrogate suspects without first warning them about their Miranda rights.
Physiological evidence and testimony are two distinct sources of information, and both are critical for validating the prosecution’s case. But in this stage of a criminal investigation, defining the differences between truth and lies is exceptionally difficult.
Forensic Analysis and Laboratory Work
Forensic science is integral to investigations. Investigators submit the evidence they collect to specialized laboratories for tests and analyses. These tests and analyses involve:
- DNA tests
- Toxicology tests
- Digital evidence retrieval
- Ballistics tests
There are many professionals who assist with forensic analyses. For instance, a crime scene technician dusts for latent fingerprints, while forensic entomologists examine insect activity on corpses to provide estimated times of death.
Using these specialists allows investigators to acquire subtle or seemingly imperceptible clues. Moreover, forensic specialists help ensure criminal investigations are accurately conducted.
Advancements in technology continue to transform forensic science. Cyber forensics, automated fingerprint identification systems (AFIS), and facial recognition technology have all accelerated the processing of evidence.
Additionally, databases like the Combined DNA Index System (CODIS) and the Integrated Ballistics Identification System (IBIS®) aid in linking suspects to criminal activities.
Suspect Identification and Arrest
Using evidence and witness testimony, law enforcement agencies work to identify and locate suspects for further investigation. Throughout their investigations, they may also construct criminal profiles, conduct surveillance, and check databases such as the National Crime Information Center (NCIC). Public tips and informants might help in suspect identification as well.
Investigators are required to show reasonable suspicion for criminal charges to occur and for an arrest to take place. If a suspect is not apprehended during a crime, an investigation must be conducted to gather sufficient evidence to justify an arrest warrant.
The arresting procedures need to observe law and order. For example, police and investigators must have probable cause or a legitimate reason to believe a crime has been committed before they can get search warrants, seize property, or make an arrest.
Legal counsel should be also provided to suspects after police book them and read them their rights. Evidence collected through inappropriate methods and a lack of probable cause – such as illegal search and seizure – is invalid.
Case Preparation and Prosecutorial Collaboration
After police make an arrest, the investigation turns toward building a solid case for court. Investigators compile all direct evidence, reports, witness lists, and expert analyses into a file for the prosecution. Prosecutors review the file to decide whether to press formal charges or negotiate a plea deal.
This collaboration between detectives and legal professionals ensures that all case elements meet the standard of proof required for conviction. They prepare for preliminary hearings, grand jury sessions, and the trial.
Challenges often arise, including reluctant witnesses, conflicting evidence, or insufficient forensic results. Investigators must be persistent; sometimes, they’ll need to revisit locations or re-interview key individuals to strengthen a case.
Trial and Testimony
The partnership between prosecutors and criminal investigators plays a vital role in court proceedings. It aids in ensuring all components of a case are prepared to withstand the burden of proof necessary for a conviction. Prosecutors and investigators strategize together for the preliminary hearings, grand jury hearings, and the trial.
Interpreting the evidence is just as important as collecting it. Investigators aid prosecutors by explaining their techniques and their findings as expert witnesses during the trial.
As the prosecution builds its narrative against the accused, the defense counters at every turn by questioning the investigation and the witnesses. Procedural mistakes, like a broken chain of custody or biased testimony, create loopholes that a defense attorney can exploit.
The cross-examination is a pivotal aspect of the trial. It’s when the opposing counsel can interrogate investigators about the techniques, evidence, and reasoning behind the conclusions they’ve drawn. Arguments and explanations must be impartial, fact-based, and grounded in reality.
A trial will typically conclude with establishing a verdict of guilty or not guilty. Some cases, like the first Karen Read trial, even end in mistrials. The result of a trial ultimately reflects not only the available evidence, but also the thoroughness of the entire investigative procedure.
Post-Conviction Follow-Up and Cold Cases
The investigation can continue in some form, even after a jury's verdict and the defendant's conviction and sentencing. Either party may file appeals, which may prompt a review of old evidence or cite newly discovered information. In some instances, advancements in forensic science, such as new DNA sequencing technologies, can even provide further information and reverse a wrongful conviction for a crime.
Modern tools like genetic genealogy or advanced data analytics can also help investigators solve cold cases. These tools can deliver justice to victims and bring closure to their families, even decades after their cases went cold.
Still, closing any criminal case requires investigators to maintain detailed, accurate, accurate records and store evidence securely. The integrity of a case must be protected from the very beginning all the way to post-conviction investigations.
Investigative Techniques Form the Bedrock of Our Justice System
An effective investigation requires a blend of science, legal expertise, and human insight. The consequences of mistakes can be life-altering. On the other hand, well-executed investigations not only enhance public trust, but also bring justice.
Criminal Justice Bachelor's Degrees at AMU
For students interested in learning more about the criminal investigation process, American Military University (AMU) offers these degrees:
The courses in these degree programs examine a wide range of topics surrounding police work, criminal law, and the U.S. legal system. Courses offered in this program include criminal investigation, ethics in criminal justice, U.S. law enforcement, and the criminal legal process.
Learners may tailor their studies by selecting a concentration. To suit their professional goals, they can focus on a particular discipline, including digital forensics, organizational law enforcement leadership, or maritime law enforcement.
For more information, visit AMU’s criminal justice degree program page.
Note: These degree programs are not designed to meet the educational requirements for professional licensure or certification in any country, state, province or other jurisdiction. These programs have not been approved by any state professional licensing body and does not lead to any state-issued professional licensure.
The Reid Technique is a registered trademark of John E. Reid & Associates, Inc.
IBIS is a registered trademark of Ultra Electronics Forensic Technology, Inc.
Dr. Matthew Loux is an assistant professor at American Public University. He holds a bachelor’s degree in criminal justice and law enforcement administration and a master’s degree in criminal justice administration from the University of Central Missouri State. In addition, Matt has a doctoral degree in management from Colorado Technical University and is pursuing a Ph.D. in educational leadership and administration at Aspen University. He is a Certified Financial Crimes Investigator, a Certified Fraud Specialist, and a Certified Fraud Examiner.
