The Techniques Used To Solve Criminal Investigations Criminology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Forensics plays a vital role in solving crimes that would otherwise go unsolved. I intend to explore in detail how to prepare and enter crime scenes from every angle of forensics and how to collect each part of evidence correctly and securely. Often, this type of work is not recognized for its tedious operation and its effectiveness, if carried out correctly, in gaining in a conviction. Fingerprint, blood, trace evidence, photography, and ballistic collections all can play a vital role in a crime scene. Each field requires one to be educated and well trained in their area of expertise and equipped to utilize their training in all scenarios. One must be thorough, organized, patient, and detail oriented enough to properly move through a crime scene. I will explain how important each field of forensics is, the training required for each field, and explain in detail their tools and their proper operations. Different patterns will be explored and defined and each forensic category will prove to be just as important as the other. Forensics has become known as the voice of a crime scene and the information gained from this I will prove this to be true.


Forensics is a tedious field of work often not accredited enough for its hard work and dedication. The world of forensics has aided prosecutors in numerous of convictions across America using DNA, fingerprint, trace, ballistic and photography evidence. However, each forensic specialist must be able to carry out the proper procedures for preserving evidence. One must be well-trained and thorough in order to prevent contamination. A simple mistake can cost a prosecutor a conviction of a brutal criminal. Therefore, protocols must be in place in to collect and preserve all evidence regardless of its importance. The field of forensics, regardless of one's specialized area, can prove to be rather challenging but with the proper knowledge and training one can excel.

Education and Roles

Police Officers

Police officers are often the first to arrive to a crime scene. Though, they are usually without a degree in a specialized area, police officers are typically well-trained in gaining control of a scene and preserving its contents. During their police academy, officers are taught the scope of law and searches. Therefore, they possess the knowledge of what they are permitted to look for. The police academy selects its candidates carefully as follows:

Must be 21 years of age prior to entry to the academy.

Must possess a high school diploma or GED.

Must have a clean criminal record.

Must pass a credit check.

Must be physically fit.

If the candidate passes these first few steps they are considered for the next phase of testing. This often includes a polygraph, medical evaluation, and a board review. If the candidate satisfies all of these categories then they will be offered a spot within the police academy. Within the academy, the recruits will be challenged with various scenarios to better equip them for handling possible hostile situations and various crime scenes. Each officer must be organized, detailed, and possess a collected attitude in order to be successful at their position.


Most law enforcement agencies hiring forensic investigators require a college degree. Often, police officers seek more education after graduation of the academy and the completion of their probationary period. Investigators are usually recruited within the policy agency but they also hire civilians with the proper education and experience. Many agencies like to hire their own officers since they are positive that their own officers have experience in law enforcement and crime scene procedures.

Due to the highly detailed analyzing of this position, individuals who are considering the field need to possess specific personal traits. First, the investigator needs to be very patient; their work is often tedious, time consuming and very thorough. Second, they need to have a logical mind in order to successfully reconstruct the crime with the evidence collected. Third, investigators require both excellent written and verbal communication skills, since they must often write detailed reports and testify in court. Third, they need to work well individually as well as part of a team. Most of all, investigators need to possess a strong stomach in order to be present at crime scenes and autopsies with bodies.


A coroner has a tough position since death occurs every single minute of the day. Anytime a body is present a coroner must appear to the scene in order to remove the body after the initial investigation has been performed. A person with this job is typically elected for this position and doesn't require a degree. However, the coroner has a tedious task of deciding to send the bodies to a medical examiner or morgue. Bodies requiring an autopsy or more testing will be sent to a medical examiner or forensic pathologist. The persons conducting autopsies or more thorough examinations require a doctorate degree.

Medical Examiner

A candidate in a career as a forensic pathologist should plan on taking anatomy, pathology, and physiology in four years of medical school. One may also be eligible to take forensic pathology electives at some medical schools, especially those which have forensic anthropology departments. One should also work briefly as an intern in the office of a forensic pathologist, so that they may weigh if the work environment is right for them. A candidate in this career should also plan on spending another four years as a forensic pathology intern after medical school, during which they will learn about analyzing tissue samples, how to handle ethical issues which could arise, and how to testify in court. After a brief forensic internship and board exams, one will be able to practice. The main factor in whether or not one is suited for this position is whether or not one has a strong stomach. This test will be implemented in medical as the student will be presented with the deceased in various stages of decomposition. This trains the student to be observant and collected.

Forensic Technician

Forensic technicians generally have a bachelor's degree in a specialized field of forensics. These types of fields can be blood spatter, ballistics, photography, latent prints, and general evidence collection. Depending on which state one works in they may be required to be sworn officers but not always. This job is extremely tedious and can require strange working hours and hazardous working conditions. One should also have a strong stomach as they could encounter decomposing bodies or other hazardous fumes. A forensic technician should also be physically fit as they may encounter many treacherous crime scenes that require physical stamina to access. In addition, the technician must be able to move light -footedly through various surfaces in order to preserve as much evidence as possible. Technicians also need to be detail-oriented team players. Everything needs to be collected in its proper container, sealed, and documented. The technicians must be verbal with their co-workers so they aren't collecting the same evidence which can be costly to the department possibly conducting DNA tests. As tedious and exerting as this job may be, it can be rewarding knowing that one's work can make a difference.

Crime Scene Preservation

Preliminary Investigation

The crime scene is the location where the crime occurred or where a possible crime may exist. This can include the direct area and any areas surrounding or linked to the crime itself. This can be determined by observing whether or not the suspect used a vehicle, or passed through a certain area. These areas need to be secured because these areas could contain vital evidence that can identify the suspect. The first member responding to a scene of a crime or complaint will:

1. Record the information provided by Dispatch Operations.

2. Determine if an offense has been committed and if so, the exact nature of the offense by observing all conditions, events and remarks.

3. Protect the victims involved in the incident

4. If necessary, administer first-aid and call in for medical assistance.

5. Take immediate steps to protect and preserve the scene, if any, from contamination and protect

evidence. The officer will request additional members to accomplish this requirement if necessary.

6. Determine the identity of the suspects.

7. Provide other members with information regarding the incident, wanted persons, vehicles, and

direction of travel.

8. Locate and identify the witnesses.

19. Conduct the arrest of the suspects if possible.

10. Obtain oral and written statements from the victims, witnesses, and from the suspect if


11. Arrange for the collection of evidence.

12. Accurately and completely record all information on the appropriate forms.

"When conducting an investigation, members will develop pertinent information through available resources which may include, but not limited to; witnesses, victims, informants, physical evidence, known Modus Operandi (MO) and suspects associated with the investigation." (Schiro, Protecting the Crime Scene, 2009, p. 2)

After the entire list has been completed it can be determined if forensics is needed in order to collect evidence or conduct scientific reconstructions. If forensics is needed, an entry point will need to be established so a log of all persons entering can be recorded.

Securing the Scene

Most police investigations begin at the scene of a crime. The scene is simply defined as the location in which the incident took place. The first officer on the crime scene should properly protect the evidence. The entire investigation relies on the first person on the scene being able to properly identify, isolate, and secure the scene. The scene should be secured by establishing a restricted perimeter. This is done by using some type of tape or barrier. The purpose of securing the scene is to restrict access and prevent evidence destruction and cross-contamination.

There are certain personnel duties and responsibilities which are necessary in almost any crime search operation. Those outlined concentrate on the ones which are typically crucial to ensure that searching for evidence is conducted in an organized fashion. One person may have more than one specific duty. However, whatever the duty may be, the proper courses of action to initiate securing a crime scene are as follows:

Take control of scene on arrival.

Determine extent to which scene has thus far been protected.

Ensure adequate scene security.

Obtain information from personnel who have entered scene and have knowledge relative to its original conditions and document who has been at scene.

Take extensive notes.

Keep out unauthorized personnel and begin recording who enters and leaves the area.

Once the scene is secured, the restrictions should include all nonessential personnel. An investigation may involve a primary scene as well as several secondary scenes at other locations. On major scenes a safe space or comfort area should be designated at the crime scene to brief investigators, store needed equipment, or as a break area. This ensures that the scene is not contaminated with food or cigarette butts. In addition, the personnel will do a better job collecting evidence if they have frequent breaks.

"In incident management, the protocol that is being taught today identifies a three layer or tier perimeter. The outer perimeter is established as a border larger than the actual scene, to keep spectators and nonessential personal safe and away from the scene, an inner perimeter allowing for a command post and comfort area just outside of the scene, and the core or scene itself." (Schiro, Protecting the Crime Scene, 2009, p. 6) This ensures a proper functioning crime scene with enough space and comfort for all of those that may be working a crime scene.

Preservation of Evidence

All evidence must be inventoried and secured to preserve its integrity. Evidence admissibility in court is dependent upon an unbroken chain of custody. It is important to demonstrate that the evidence presented at trial is the same evidence collected at the crime scene, and that access was controlled and documented. There are no exceptions to this policy.

The chain-of-custody rules are vital for an investigator. For example, in a rape case, the victim is typically transported to another location to have a sexual assault examination performed. Many jurisdictions have established teams to perform these examinations. The examination involves the collection of the victim's clothing, hair samples, swabs for body fluids, and documentation of bruising and bites marks. The materials collected are packaged by the authorized personnel. Proper evidence packaging includes appropriate packaging and labeling of all items, ensuring each item properly sealed and marked, and ensuring the correct information is recorded on label and cross-reference documentation.

The evidence is turned over to the investigator for submission to a department's property and evidence section. Each individual, requesting the evidence, signs the chain of custody document, no exceptions. The chain of custody report will identify each individual contributing to the analysis or any examination of the materials. In addition, this chain of custody method can help determine if evidence was properly handled and not contaminated.

"Once the analysis is complete, the evidence is either returned to the submitting agency or stored by the laboratory. The chain of custody will document this disposition. All law enforcement reports, photographs, lab analysis reports, and chain of custody documents are kept in the case file, which can be made available to the prosecution and is subject to discovery by defense counsel." (, 2009, p. 2)

The easiest way to ensure the safe guard of evidence is to limit the number of individuals handling evidence, confirm that all names, identification numbers, and dates are listed on the chain of custody documents, and ensure that all evidence packaging is properly sealed and marked prior to submission.


Blood Stains

Videotape evidence can be an excellent source for documenting bloodstains at a crime scene. If a video camera is best used after the initial walk through. This is to record the evidence before any major changes have occurred at the scene. Videotape provides a perspective on the crime scene that cannot be as easily seen in photographs. It allows for a more natural viewing to which people can easily relate, especially in demonstrating the structure of the crime scene and presenting those details in court.

As with any crime scene, it's essential that still photographs are taken to document the crime scene and any blood evidence. If a video camera is available, then still photography should be the second step in recording the crime scene. Photographs can demonstrate the same type of things that the videotape does, but crime scene photographs can also be used to record close up details, record objects at any scaled size, and record objects at actual size. These measurements and recordings are more difficult to achieve with videotape.

Blood evidence can be photographed from many angles and with various films. However, color print film should be used for lighter surfaces and infrared film should be used for documenting bloodstains on dark surfaces. "Scaled photographs (photographs with a ruler next to the evidence) must also be taken of items in cases where size relevance is significant or when direct comparisons will be made, such as with bloody shoeprints, fingerprints, or high velocity blood spatter patterns." (Schiro, Bloodstain Photography, 2008, pp. 1-3) The overall pattern on the wall, including a yard stick as a scale, should be the procedure for documenting blood stains on a surface. By using a yardstick, the original blood spatters can be viewed at their actual size and placed in their original positions. Measurements and projections can then be made to determine the spatters' points of origin.

Motor Vehicle Crash

Scenes of motor vehicle collisions, and scenes involving crashes of any kind, should also be photographed using the "big picture, mid-range and close-up principle." (Pearson, 2007, pp. 1-2) The photographs must show the relationships of each vehicle to the other, the view each driver had to the point of impact; the direction from which each driver came, debris and marks on the roadway, views from the points witnesses observed the crash, technical photographs showing damage to the vehicles. "The damage to a vehicle must be photographed from at least two opposing diagonals and through the two axes of the vehicle, as a minimum." (Pearson, 2007, pp. 1-2) The flash should be used to fill in shadows within damaged areas. Despite the terrain and the positions and angles of vehicles, it's important to keep the camera horizontal at all times.

Latent Prints

Latent Print evidence can be divided into two categories, porous and non-porous. Porous evidence such as paper, unfinished wood, and cardboard are normally better for the preservation of prints because latent print residue can soak into the surface. Non-porous evidence such as plastic, glass, metal, and foil are much more fragile because the latent print residue may just be lying on the surface. Even the slightest handling can wipe away a latent print on non-porous surfaces.

"The most common type of surface examined for latent prints is the smooth, nonporous, nonferrous surface such as glass, painted surfaces, and some hard plastics." (BAE Systems, 2007, p. 1) The first step should be a close examination of the surface for latent prints. This step can include the use of a flashlight better viewing. It might also use the hot breath technique to fog the surface. Any prints visually observed should be photographed before proceeding to the next step.

The second step should be an examination with a "Forensic Light Source, including photography of any prints visible through inherent luminescence." (BAE Systems, 2007) Following this preliminary examination, the surface should be super-glue fumed. Again, an examination and photography should be used before proceeding. The next step would be to lightly dust the surface, first using nonmagnetic powder followed by powdering with magnetic powder using the hot breath technique and photographing any additional prints before lifting them. Finally, dye staining with a fluorescent dye should be done last, followed by photography. By using all of these methods correctly and in the proper order, one could be confident of recovering any latent prints of value on the surface.

"The second most common type of surface examined for latent prints is a porous surface such as paper or cardboard." (BAE Systems, 2007, p. 1) Again, the first step should be a careful examination with photographs taken of any visible latent prints. Next, a fluorescent examination should be made for inherent luminescence, again accompanied by photography of any prints observed.

The next step should be iodine fuming. "Although generally considered relatively unproductive, iodine fuming offers the advantage of temporarily making the prints visible without permanently altering the evidence." (BAE Systems, 2007, p. 2) Any prints developed should again be photographed before proceeding. Next, magnetic powder may be used but should only be used on very fresh latent prints. Again, prints should be photographed.

Following these methods, various liquid chemicals would be used. "First, DFO would be applied, followed by a fluorescent examination and photography. Then, traditional Ninhydrin would be used, followed by photography. Finally, Physical Developer would be used. At this step, Physical Developer still frequently develops latent prints completely undetected by all of the previous methods." (BAE Systems, 2007, p. 2)

DNA Collection and Preservation

Crime scene technicians should be aware of important issues involved in identifying, collecting, transporting, and storing DNA evidence. If DNA evidence is not initially identified at the crime scene or on the victim, it may not be collected, or it may become contaminated. However, not all evidence can be collected at the crime scene and may require the help of a medical professional to extract it.

In the interest of preserving evidence, victims of sexual assault should not change clothes, shower, or wash any part of their body after the assault. Such evidence as semen, saliva, and skin cells may be found on clothing, bedding, under fingernails, or in the vaginal, anal, or mouth region. In addition, the victim should not urinate since wiping can alter the evidence as well. The urine following a sexual assault can contain a possible drug given to the victim to aide in the assault.

Evidence on or inside a victim's body should be collected by a physician or sexual assault nurse examiner. A medical examination should be conducted immediately after the assault to treat any injuries, test for sexually transmitted diseases, and collect forensic evidence, such as fingernail scrapings and hair. Typically, the vaginal cavity, mouth, anus, or other parts of the body that may have come into contact with the assailant are examined.

The examiner should also take a reference sample of blood or saliva from the victim to serve as a control standard. Reference samples of the victim's head and pubic hair may also be collected if hair analysis is required. "A control standard is used to compare known DNA from the victim with that of other DNA evidence found at the crime scene to determine possible suspect." (, 2009)

Before transporting and storing evidence that may contain DNA, it is important to keep the evidence dry and at room temperature. However, sometimes it is not possible to transport completely dry objects. Therefore, a hair dryer can assist in drying the evidence. If the evidence can't be dried on the scene then the object should be laid flat and secured in a paper bag. Upon arrival to the designated lab area, these objects should be dried immediately. Once the evidence has been dried, it should be sealed, labeled, and stored in a way that ensures proper identification of where it was found and proper chain of custody. Never place evidence that may contain DNA in plastic bags because plastic bags will retain damaging moisture and thus cause contamination.


Ballistics can be defined as the study of the dynamics of projectiles, the flight characteristics of projectiles, the study of the functioning of firearms, and the study of the firing, flight, and effects of ammunition. Ballistics is divided into two categories; internal and external. Internal ballistics, a subfield of ballistics, is the study of a projectile's behavior from the time its propellant's igniter is initiated until it exits the gun barrel. This is a very complicated subject as it entails the explanation of what happens inside the gun. External ballistics is the science of ballistics that deals with the behavior of a non-powered projectile in flight. External ballistics is most often associated with firearms, and deals with the behavior of the bullet after it exits the barrel and before it hits the target.

Internal ballistics describes what happens in the chamber of a rifle or handgun when it is fired and how the case and bullet are affected. Each gun has a specific "trademark" and leaves a special imprint on the bullet when expelled from the chamber. Of course this imprint can vary depending if the bullets are manufacturer made or reloaded shells. By locating the expelled shells the ballistic expert can determine what caliber gun may have been used. After identifying the correct caliber the experts can begin their testing. A reconstruction of the crime scene will be reenacted using the exact caliber weapon. A check in the data base of gun ownership could reveal possible suspects and their guns can be tested to see if the imprint matches that of the shells that were discovered at the crime scene.

External ballistics is a complicated subject but much easier to define. External ballistics explains the main forces acting on the projectile. These are defined as gravity, drag and wind. Gravity pulls a downward acceleration on the bullet, causing it to drop from the original height. Drag or the air resistance decelerates the bullet with a force exponentially proportional to the square of the velocity. Wind makes the bullet deviate from its trajectory. During flight, gravity, drag and wind, it will have a major impact on the path of the bullet, and must be accounted for when predicting how the bullet may have traveled. This is extremely important in crime scenes where investigators are not exactly sure where the shooter came from. This can also aide in determining how tall the shooter may have been or if they may have been in sitting or standing position.

Blood Spatter Analysis

Blood is often discovered during crimes of violence.  It is often possible to reconstruct one or more possibilities of what may have occurred by interpreting certain bloodstain patterns.    To achieve this, it is essential that all available bloodstains be examined, either at the scene of the crime or from good quality photographs.  Their overall size, shape and distribution must be examined overall and not just in isolated areas. A scene containing blood splatter can tell a story all on its own.

Once it has been determined that the blood is human, its pattern can be investigated. However, most law enforcement officers do not do this. Typically, specialists are called in to evaluate, photograph, and collect the blood evidence. The specialist will try to determine what the position and shape indicate. The specialists may take measurements to determine the trajectory path as well as conduct several controlled experiments. These experiments will use surface materials like those found at the scene. The specialists will use blunt objects and hit the fake person at various angles. Fake blood will erupt with each blow and thus leaving a distinct pattern. This procedure can also be practiced at various heights to determine the attacker's possible accurate height. This is also done by using a string method that places somewhat reenacts where the victim may have been when the point of impact occurred. The strings pointing outward reflect exactly where the blood patterns should have landed if consistent with the specialist's theory. The general rules to follow in blood spatter are as follows:

"The smaller the size of blood splatters, the greater the energy required to produce them.  Low, medium, and high velocity impact spatter may be identified by their respective sizes but exceptions must also one considered.

Diameter of a large bloodstain will be of little value in estimating the distance a drop of blood has fallen prior to impact.

When considering the shape of a bloodstain for use in calculating its angle of impact, only a sharp, well-defined bloodstain should be used for measuring its width and length.

Directionality of a blood drop while in flight is usually obvious from the geometry of its resulting bloodstain.  The pointed end indicates the direction of travel prior to impact on a surface.  Directionality may also be determined when edge scallops appear on only one side of a bloodstain.  

When a dozen or more small bloodstains are present in a recognizable pattern, their size may allow a prediction as to the energy that was required to produce them.  

When the preponderance of dozens of individual bloodstains are approximately 1mm or more in diameter, they are consistent with having been produced as a result of a medium velocity impact.  Most often they would result from a beating or stabbing.

The shape of a bloodstain is a function of the angle at which it impacts a surface.  Perfectly round bloodstains result from a ninety degree impact.  The angle of impact of an elliptical bloodstain may calculated from its length to width ratio.

Bloodstains may often be lifted from the surface upon which they have been deposited.  The harder and smoother the surface the more likely they may be successfully lifted.

When measurements and angles are used to establish the origins in space, not only will the actual origin be somewhere below the point or points of convergence, but it must be remembered that the investigator is determining a spacial volume and not a small point of origin.

Sobriety of the victim will have no significant effect on how bloodstain patterns are produced.  A high blood alcohol level is of no concern to the interpretation of bloodstain patterns.

When blood is projected upward with sufficient force to strike a ceiling, it will almost always be the result of a gunshot having an upward trajectory.  Such a trajectory is more often the result of a suicide rather than a homicide." (Brazoria County Interpretations, 2008, pp. 1-4)

Trace Evidence Collection

Trace evidence is left at a crime scene when one object touches another. This type of evidence is quite small, but large enough to measure. Some examples of trace evidence are scrape marks, fingerprints, hair, fibers, soil, tool marks, paint chips, and even glass. This evidence is quite small but can lead a case in the right direction if no other leads are present.

Investigators must use caution when entering crime scenes to avoid disturbing or destroying trace evidence. They must also take steps to avoid contaminating the crime scene by accidentally depositing things that could be mistaken for evidence, such as cigarette butts, hairs, and chewing gum. There are various ways this evidence can be collected. Each task is tedious and requires the proper handling and packaging in order to preserve its integrity. Each task is defined as follows:

Scraping is a tedious way to collect trace evidence. Often, a scalpel is used in this process to collect blood spatter or any other evidence that could be dried to a surface. The evidence is scraped into a paper sleeve and then labeled and sealed properly.

Picking is another great way to collect trace evidence. Typically needle nose pliers are used to pick at fibers or hairs left behind. This is a great way to pick evidence off of a deceased victim without disturbing any other potential evidence. The evidence is then placed into paper sleeve, labeled and sealed.

Vacuuming is another effective way of gathering trace evidence. This process is often used when soil, glass, or possible jewelry are imbedded within a carpet or upholstery. This special vacuum is equipped with its own plastic container that traps all evidence sucked through the vacuuming process. This container can be emptied into a paper sleeve or bag and labeled correctly once completed.

Lifting is an effective way to collect trace evidence upon a victim or in the general crime scene. A piece of specialized tape can pull up hundreds of pieces of hairs and fibers that can lead to the discovery of a suspect. Of course, this evidence should be preserved into a Petri dish since tape sticks to paper and plastic thus can destroy vital evidence.

Combing is an effective way to search a victim for possible trace evidence. Often, combing can reveal foreign hairs and debris that can aid the case in a possible lead. A deceased victim may have dandruff or fibers within their hair that may not be visible at a first glance. The foreign materials discovered should be sealed in a paper sleeve and labeled correctly.

Clipping is another way to collect trace evidence from a victim. The victim's nails could contain DNA of their attacker. Parts of the fingernails are clipped in order to preserve this possible evidence. The nail clippings are then stored in a paper sleeve, sealed, and labeled correctly.


Forensics is a tedious field of work often not accredited enough for its hard work and dedication. The world of forensics has aided prosecutors in numerous of convictions across America using DNA, fingerprint, trace, ballistic and photography evidence. However, each forensic specialist must be able to carry out the proper procedures for preserving evidence. One must be well-trained and thorough in order to prevent contamination. A simple mistake can cost a prosecutor a conviction of a brutal criminal. Therefore, protocols must be in place in to collect and preserve all evidence regardless of its importance. The field of forensics, regardless of one's specialized area, can prove to be rather challenging but with the proper knowledge and training one can excel. The specialists placed into these roles have to utilize extreme caution and follow protocol accordingly in order to preserve all evidence and its complete integrity.