The Inner Workings of Crime Scene Investigation

On TV series such as "CSI," audiences witness investigators uncovering and gathering evidence at crime scenes, with blood seemingly appearing out of nowhere and every nearby individual being swabbed. Many assume they understand the procedure, and there's talk that criminals are gaining an edge by learning forensic techniques from these shows.

But is Hollywood's portrayal accurate? Do crime scene investigators analyze their DNA samples in the lab? Do they interrogate suspects and apprehend criminals, or is their role solely focused on gathering physical evidence? In this article, we'll explore the true process of how a CSI handles a crime scene, offering insights from a firsthand responder at the Colorado Bureau of Investigation.

Fundamentals of Crime Scene Investigation

Crime scene investigation sits at the intersection of science, logic, and the legal system. "Processing a crime scene" is a meticulous and time-consuming procedure that requires detailed documentation of the scene's state and the gathering of any physical evidence that might shed light on the events and identify the perpetrator. Each crime scene is unique, with no standard set of evidence or uniform investigative method.

At a crime scene, a CSI might carefully collect dried blood from a windowpane, ensuring not to touch the glass to preserve potential latent fingerprints. They might use tweezers to remove hair from a victim's jacket, being cautious not to disturb any mysterious white powder (possibly cocaine) in the sleeve's folds. They could even use a sledgehammer to break through a wall suspected to be the source of a foul odor.

While collecting evidence, the CSI must also consider the broader picture. The primary objective is to secure a conviction. As they meticulously gather evidence—like scraping blood without smearing prints or lifting hairs without losing trace evidence—they must also ensure the evidence remains intact for lab analysis, which can help reconstruct the crime or identify the culprit. Additionally, they must navigate legal requirements to ensure the evidence is admissible in court.

The crime scene investigation process kicks off when the CSI unit is contacted by police officers or detectives at the scene. The general workflow follows a structured approach:

Each CSI unit has its own approach to dividing field work and lab work. Field activities are termed crime scene investigation (or crime scene analysis), while lab activities fall under forensic science. Not all CSIs are forensic scientists; some focus solely on field work, collecting evidence and transferring it to the lab. In such cases, the CSI must still have a solid grasp of forensic science to recognize the value of different types of evidence. However, these roles often overlap in practice.

Joe Clayton, a primary crime scene responder at the Colorado Bureau of Investigation (CBI), brings 14 years of field experience and expertise in specific areas of forensic science. Clayton explains that his involvement in lab analysis depends on the type of evidence collected:

Crime scene investigation is a complex process. It all begins with scene recognition.

At the Crime Scene: Scene Recognition

When a CSI arrives at a crime scene, they don’t immediately start collecting evidence. The purpose of the scene recognition phase is to comprehend the scope of the investigation and devise a structured method for locating and gathering evidence. At this stage, the CSI relies solely on their eyes, ears, nose, paper, and pen.

The initial step is to determine the boundaries of the crime scene. For instance, in a homicide case where the victim was killed in their home, the crime scene might include the house and its immediate surroundings. Does it extend to vehicles in the driveway? Is there a blood trail leading down the street? If so, the crime scene could encompass the entire neighborhood. Securing the crime scene—and any additional areas that may later be identified as part of it—is critical. A CSI typically has only one opportunity to conduct a thorough, uncontaminated search. Furniture may be moved, rain could destroy evidence, detectives might handle items during later searches, and evidence could be compromised.

Typically, the first responders secure the core area—the most evident part of the crime scene where the majority of evidence is concentrated. When the CSI arrives, they expand the secured area beyond the core scene, as it’s easier to reduce the scene’s size later than to expand it. This precaution prevents interference from press vehicles or bystanders who might disrupt areas later identified as part of the crime scene. Securing the scene involves setting up physical barriers like crime scene tape, police vehicles, or sawhorses, and removing non-essential personnel. A CSI may also establish a "safe zone" near the scene where investigators can regroup and strategize without risking evidence contamination.

After defining and securing the crime scene, the CSI involves the district attorney. If any part of the scene could involve privacy concerns, the CSI must obtain search warrants. Evidence is only valuable if it’s admissible in court, so a cautious CSI rarely proceeds without a warrant.

With a search warrant in place, the CSI conducts a walk-through of the crime scene, following a pre-planned path to minimize evidence disturbance. During this initial assessment, they note time-sensitive details: weather conditions, time of day, unusual smells (e.g., gas or decomposition), sounds (e.g., dripping water or a smoke alarm), and anything out of place, such as a chair blocking a door or missing pillows. They also identify and address potential hazards, like gas leaks or aggressive animals near the body.

Based on observations during the recognition phase, the CSI calls in specialists or additional equipment. For example, a t-shirt caught in a tree might require a scissor lift, while blood spatter on the ceiling or maggot activity on a body necessitates on-site analysis by experts. Mr. Clayton, an expert in blood spatter analysis, would handle such tasks alongside his investigative duties.

During this phase, the CSI consults with first responders to determine if they touched anything and gathers information to refine their approach. Detectives conducting witness interviews may provide clues, such as the victim being on the phone before the incident, pointing the CSI to evidence like a Caller ID unit. If a neighbor reports hearing a struggle followed by running water, the CSI might search for blood in bathrooms or kitchens. Most CSIs, including Mr. Clayton, do not interview witnesses, as their expertise lies in physical evidence. They rely on detectives for witness accounts.

The CSI leverages the information gathered during scene recognition to devise a tailored strategy for the specific crime scene. There is no one-size-fits-all method for crime scene investigation. As Mr. Clayton notes, the approach for a mass casualty event like the Columbine High School shootings (where he was involved) differs significantly from that for a single-victim crime like a car rape. Once the CSI formulates a plan to collect all relevant evidence, the next step is to meticulously document every detail of the scene, enabling others to reconstruct it accurately. This marks the scene-documentation phase.

Crime Scene Documentation

The objective of crime-scene documentation is to produce a visual record that enables the forensics lab and prosecuting attorney to reconstruct an accurate depiction of the scene. The CSI employs digital and film cameras, various film types, lenses, flashes, filters, a tripod, sketchpads, graph paper, pens, pencils, measuring tape, rulers, and a notepad during this phase. Additionally, they may use a camcorder and a camera boom.

Scene documentation takes place during a second walk-through, following the same path as the initial assessment. If multiple CSIs are present (Mr. Clayton has worked both solo and as part of a large team), tasks are divided: one CSI photographs, another sketches, a third takes detailed notes, and a fourth may conduct a video walk-through. If only one CSI is available, they handle all these responsibilities.

Notes

Taking notes at a crime scene requires more than basic observation. A CSI is trained in scientific observation. While a layperson might describe a large, brownish-red stain on the carpet as "blood spreading from the corpse," a CSI would note "large, brownish-red fluid spreading from the underside of the corpse." This fluid could be blood or decomposition fluid, which can resemble blood. Mr. Clayton emphasizes that opinions and assumptions have no place in crime scene investigation. A CSI records only factual observations, avoiding conclusions.

Photographs

CSIs photograph every detail before handling or relocating any evidence. The medical examiner refrains from touching the body until the CSI completes photographing both the corpse and its surroundings. Three types of photographs are taken: overviews, mid-views, and close-ups.

Overview shots capture the broadest perspective of the entire scene. For indoor scenes, this includes:

These final shots may help identify potential witnesses or even suspects. In some cases, criminals return to the crime scene, especially in arson incidents.

Mid-range photos follow, focusing on key evidence within its context. These images show the evidence's location in the room and its proximity to other pieces of evidence.

Finally, the CSI captures close-ups of individual evidence items, highlighting serial numbers or unique identifiers. For these shots, a tripod and professional lighting are used to ensure maximum detail and clarity, which are crucial for forensic analysis. A second set of close-ups includes a ruler for accurate scaling.

Every photograph taken by the CSI is recorded in the photo log. This log details each photo's number, description, location, time, date, and other relevant information. Without a thorough photo log, the images lose much of their investigative value. For example, during the John F. Kennedy assassination investigation, the lack of detailed descriptions in autopsy photos made it difficult to differentiate between entrance and exit wounds.

Sketches

In addition to photographs, CSIs create sketches to illustrate the entire scene and specific areas requiring precise measurements. Sketches can span multiple rooms and show the relationship between pieces of evidence. Details like door frame height, room dimensions, distances between objects, and the size of specific features (e.g., a hole in the wall) are included to provide a comprehensive visual record.

Video

Scene documentation may also involve a video walk-through, particularly in high-profile cases like serial killings or multiple homicides. A video recording provides a clearer sense of the crime scene's layout, such as the time it takes to move between rooms or the number of turns involved. It can also highlight details initially overlooked as investigators may not have known to look for them. During the walk-through, the CSI records the entire scene and surrounding areas from all angles, accompanied by a continuous audio narration.

Once the CSI has thoroughly documented the crime scene in its original state, the next step is to collect evidence. This is when physical interaction with the scene begins.

Finding Crime Evidence

The objective of the evidence-collection phase is to locate, gather, and preserve all physical evidence that can help reconstruct the crime and identify the perpetrator in a way that is admissible in court. Evidence can take various forms. Common types of evidence a CSI might encounter at a crime scene include:

Guided by their theories of the crime, CSIs conduct a systematic search for incriminating evidence, documenting every detail. If a body is present, the search typically begins there.

Examining the Body

A CSI may gather evidence from the body either at the crime scene or after it reaches the morgue. In both scenarios, they conduct a visual inspection of the body and its surroundings, capturing photographs and detailed notes.

Before relocating the body, the CSI records specific details, such as:

After moving the body, the CSI repeats the examination on the other side. They may also measure the body's temperature and the room's ambient temperature to estimate the time of death (though this is often unreliable due to the body's unpredictability and numerous variables). Additionally, they collect fingerprints either at the scene or at the medical examiner's office.

Once the CSI finishes documenting the body and its immediate surroundings, technicians wrap the body in a white cloth and place paper bags over the hands and feet for transport to the morgue for an autopsy. These measures preserve any trace evidence. The CSI often attends the autopsy, taking additional photos or videos and collecting tissue samples from major organs for lab analysis.

Examining the Scene

A CSI can select from several search patterns to ensure thorough coverage and optimal use of resources.

The inward spiral search: The CSI begins at the outer edge of the scene and moves systematically toward the center. This method is particularly effective when only one CSI is available.

The outward spiral search: The CSI begins at the center of the scene (or at the body) and moves outward in a spiral pattern.

The parallel search: The CSI team forms a straight line and walks uniformly from one end of the crime scene to the other, ensuring thorough coverage.

The grid search: This method involves conducting two parallel searches, with the second offset by 90 degrees from the first, ensuring comprehensive coverage.

The zone search: In this approach, the CSI leader divides the crime scene into sections, assigning each to a team member. Members may later switch sections to double-check for thoroughness.

While examining the scene, a CSI focuses on details such as:

The collection of physical evidence is a meticulous process. Each item must be preserved, tagged, and logged immediately for the crime scene record. Depending on conditions and resources, evidence may be collected at the scene or in the lab. For example, Mr. Clayton never develops latent fingerprints on-site, always sending them to the lab for controlled processing. In the next section, we'll explore specific evidence collection methods.

Evidence Collection

When collecting evidence from a crime scene, the CSI focuses on several key objectives: Reconstructing the crime, identifying the perpetrator, preserving evidence for analysis, and ensuring it is collected in a manner that will hold up in court.

Trace Evidence

Trace evidence can include gunshot residue (GSR), paint fragments, chemicals, glass, and illegal drugs. To gather such evidence, a CSI may use tweezers, sealed plastic containers, a filtered vacuum device, and a knife. They also carry a biohazard kit with disposable latex gloves, booties, face masks, gowns, and a biohazard waste bag.

In gun-related crimes, the CSI collects clothing from the victim and anyone present at the scene for GSR testing. GSR on the victim suggests a close-range shot, while GSR on others may point to a suspect. All clothing is placed in sealed paper bags for lab transport. If illicit drugs or unknown powders are found, the CSI collects samples with a knife, sealing each in a sterile container. The lab identifies the substance, checks its purity, and detects trace components, which can reveal drug possession, tampering, or potential lethality.

Much trace evidence is discovered in the lab by shaking out items like bedding, clothing, towels, and couch cushions from the scene. At the CBI Denver Crime Lab, this is done in a sterile room over a large, white, paper-covered slab.

Technicians then send the trace evidence to the appropriate department. At the Denver Crime Lab, items like soil, glass, and paint remain in the trace-evidence lab, while illegal drugs and unknown substances go to the chemistry lab, and hair is sent to the DNA lab.

Body Fluids

Body fluids at a crime scene may include blood, semen, saliva, and vomit. To identify and collect these, a CSI might use smear slides, a scalpel, tweezers, scissors, sterile cloth squares, a UV light, protective eyewear, and luminol. They also use a blood collection kit to gather samples from suspects or living victims for comparison.

If the victim is deceased and blood is present, the CSI collects a blood sample by submitting clothing or using a sterile cloth square with distilled water to extract blood. Blood or saliva from the body may belong to someone else, and the lab conducts DNA analysis for future comparisons with suspect samples. The CSI also scrapes the victim's nails for skin, which may contain the suspect's DNA if a struggle occurred. For dried blood on furniture, the CSI may send the entire piece to the lab. If blood is on immovable surfaces like walls or bathtubs, it is scraped into a sterile container using a scalpel. Luminol and a UV light can reveal washed-off blood.

Blood at the scene may also show blood spatter patterns. These patterns can indicate the weapon used. For example, a "cast-off pattern" results from a weapon like a baseball bat striking a blood source and swinging back, leaving large, teardrop-shaped droplets. This suggests multiple blows, as the first strike usually doesn't contact blood. A "high-energy pattern," with many tiny droplets, may indicate a gunshot. Blood spatter analysis reveals the blood's origin and the number of incidents creating the pattern. The CSI photographs the pattern and may consult a blood-spatter specialist.

Hair and Fibers

A CSI uses combs, tweezers, containers, and a filtered vacuum to collect hair or fibers. In rape cases with live victims, the CSI accompanies the victim to the hospital to collect hairs or fibers found during the medical exam. All hair and fiber evidence is sealed in separate containers for lab transport.

A CSI might find carpet fibers on a suspect's shoes, which the lab can compare to fibers from the victim's home. Hair DNA can identify or exclude suspects through comparison. Hair on a tool or weapon can link it to the crime. The lab can determine if the hair is from a human, dog, cow, etc., and if human, identify the race, body part, whether it fell out or was pulled, and if it was dyed.

Fingerprints

Tools for fingerprint recovery include brushes, powders, tape, chemicals, lift cards, a magnifying glass, and Super Glue. Fingerprints can identify victims or suspects. Types of prints a CSI might find include:

Prints may be left on porous or nonporous surfaces. Porous surfaces like paper, unfinished wood, and cardboard hold prints, while nonporous surfaces like glass, plastic, and metal also retain them. A CSI searches for latent prints on surfaces the perpetrator likely touched, such as a doorknob after a forced entry. Breathing on a surface or using strong light can temporarily reveal latent prints. Touching a surface with bare hands, like turning a doorknob, can destroy prints. Proper recovery methods are essential to preserve latent prints on nonporous surfaces.

Powder (for nonporous surfaces): Metallic silver or velvet black powder is used, depending on the surface color. The CSI gently applies the powder in circular motions until a print appears, then brushes along the ridges. After photographing the print, they lift it with clear tape and place it on a fingerprint card of a contrasting color.

Chemicals (for porous surfaces): Iodine, ninhydrin, or silver nitrate is sprayed or dipped onto the surface to reveal latent prints.

Cyanoacrylate (Super Glue) fuming (for porous or nonporous surfaces): The CSI heats Super Glue to around 120 F in a metal plate, then places it with the object in an airtight container. The fumes reveal the latent print without damaging the material.

Footwear Impressions and Tool Marks

A latent fingerprint is a two-dimensional impression, while a footwear mark in mud or a tool mark on a window frame is three-dimensional. If the object with the impression cannot be sent to the lab, the CSI creates a cast on-site.

A casting kit typically contains various casting compounds (dental gypsum, silicone rubber), snow wax (for snow impressions), a bowl, a spatula, and cardboard boxes to store the casts.

If a CSI discovers a footwear impression in mud, they photograph it and create a cast. They mix casting material with water in a Ziploc bag, knead it for about two minutes until it reaches a pancake batter consistency, and pour it into the impression to avoid air bubbles. After letting it set for at least 30 minutes, they carefully lift the cast and place it in a cardboard box or paper bag for transport to the lab, ensuring no trace evidence is disturbed.

For toolmark impressions, casts are less reliable for comparison than with footwear. If transporting the entire object with the tool mark isn't possible, a CSI may create a silicone-rubber cast as a best-effort solution. Tool marks at a crime scene fall into two categories:

In toolmark analysis, the lab identifies the tool type, matches it to a suspect tool, or compares tool marks to determine if the same tool was used.

Firearms

If firearms, bullets, or casings are found, the CSI wears gloves, handles the gun by the barrel (not the grip), and bags each item separately for the lab. Forensic experts can recover serial numbers and match bullets and casings to the weapon used, as well as to those from other crime scenes statewide. Using a laser trajectory kit, specialists determine the bullet's origin, firing height, and the victim's position. If bullets are embedded in walls or frames, the CSI removes the surrounding material to avoid damaging the bullet during extraction.

Documents

A CSI collects and preserves diaries, planners, phone books, or suicide notes found at a crime scene. They also submit signed contracts, receipts, torn-up letters, or other written, typed, or photocopied evidence to the lab. Document labs can often reconstruct destroyed or burned documents and detect alterations. Technicians analyze documents for forgery, match handwriting to victims or suspects, and identify the type of machine used to produce the document. They can exclude a printer or photocopier found at the scene or determine compatibility with a suspect's machine.

When a CSI finds evidence, they photograph, log, recover, and tag it. An evidence tag may include details like time, date, location, and the recovering officer's name, or a serial number linked to the evidence log. The crime scene report compiles all recovered evidence, including the photo log, evidence recovery log, and a written account of the investigation.

Analyzing the Evidence: Forensic Science

The first forensic lab in the U.S. opened in 1923 in Los Angeles. In 1932, the FBI launched its own forensic lab to assist police departments and investigative agencies nationwide. The FBI lab is among the largest globally.

The Denver Crime Lab at the Colorado Bureau of Investigation offers evidence collection and lab analysis for any Colorado police department. It also handles state-level investigations outside local jurisdiction.

Specialized departments in the Denver Crime Lab include latent fingerprints and impressions, which processes latent prints, analyzes and compares fingerprints, footwear, and tire marks, and uses the Automated Fingerprint Identification System (AFIS) to compare prints against millions in the FBI database.

The trace evidence department handles GSR analysis and identifies and compares soil, glass, fibers, and paint samples. The chemistry section analyzes and compares illegal drugs, explosives, and unknown chemicals. The computer crimes team retrieves evidence from computers and enhances audio or video evidence. The firearms and toolmark identification team identifies firearms, tests barrel patterns, determines shooting distances, and compares bullets, casings, and toolmarks. The serology and DNA section analyzes body fluids, including DNA from blood, semen, and hair for identification and comparison.

Lastly, the questioned document section detects forgery, analyzes handwriting, reconstructs destroyed documents, and identifies printers, typewriters, or copiers used to create documents.

Evidence often moves through multiple departments for analysis. Each department provides a detailed report, including results (measurements, chemical content) and expert conclusions. The CSI may compile these findings for the lead detective, or the lab may send them directly to the detective squad.

CSI vs. 'CSI'

Does Hollywood get it right? When asked if the TV show "CSI" accurately portrays his job, Joe Clayton's short answer was, "No." He explained that while the show captures some aspects of crime scene investigation, it omits and exaggerates many details for entertainment. Viewers wouldn't enjoy watching CSIs wait for search warrants or go without seeing the suspect.

Scientifically, "CSI" often misses the mark. In reality, determining a two-hour window for time of death isn't feasible. Additionally, fingerprint analysis doesn't involve scanning a print into a computer and instantly getting a suspect's photo. Fingerprint software provides potential matches, which an expert then visually analyzes to confirm a match.

Hollywood also misrepresents the investigative process. CSIs almost always require warrants before searching a scene. The only exception might be a victim's apartment if they lived alone and never shared the space. This often involves waiting—CSIs typically assess the scene, then coordinate with the district attorney and a judge to obtain warrants before starting the search.

The search focuses on evidence, not interviewing neighbors or suspects. CSIs don't handle witness interviews, interrogations, or chasing perpetrators—these tasks fall to detectives. It's also rare for a single CSI to manage an entire investigation from start to finish. Evidence collection and analysis involve multiple professionals, including CSIs, forensic experts, medical examiners, and detectives. Few CSIs have the time or expertise to handle every aspect.

According to Mr. Clayton, shows like "CSI" aren't making criminals smarter. Crime scene investigation and forensic science are always playing catch-up with criminals, not the reverse. While some meticulously plan crimes, most violent acts occur impulsively. Perpetrators are often agitated, under the influence, and lack the focus to cover their tracks thoroughly. True criminal masterminds who study forensic science to commit the perfect crime are rare.

For more information on crime scene investigation, forensic science, and related topics, explore the links below.