Crime Scene Investigation: A Practical Manual

Posted on Oct 6, 2024 in Social sciences

Manual of Practical Use

Crime Scene Visual Inspection

In a visual inspection, clues and evidence are collected to help build a clear and incontestable judgment for judges and courts. If these technical and scientific means of evidence are collected properly, if the chain of custody is maintained, and if there is adequate quality control, the obtained evidence is irrefutable. This evidence becomes an essential tool for the justice system.

Concept

The visual inspection is part of a scientific and technical research process. It aims to discover the truth concerning persons, things, or circumstances that have occurred in a particular location.

Inspect means “to examine something carefully using all the senses and the appropriate instruments.”

A police technical visual inspection is the set of observations, checks, and technical police operations carried out at the scene of a crime for investigative purposes.

The visual inspection is based on the principle of “exchange,” whereby any person who enters a location takes something and leaves something (all contact leaves a trace). Therefore, visual inspection is based on discovering, preserving, transporting, and studying the tracks, signals, signs, traces, and relics present at the scene.

Purpose of the Visual Inspection

There are four purposes of visual inspection:

1. Verify the crime occurred.
2. Identify the perpetrator.
3. Provide evidence to the Judicial Authority within the framework of criminal proceedings, which serves to support the indictment or acquittal of the suspect.
4. Serve as a basis for further investigation.

Visual Inspection Practice

From a police perspective, the visual inspection is organized around three working groups, which must act jointly and extract the necessary information with due diligence. The assembly of this information constitutes the essence of the police investigation.

These three working groups are:

A) Public Security Police

Usually the first to arrive on the scene. Their mission focuses on:

• Humanitarian action (if needed).
• Gathering prior information on the scope of the incident (and affected witnesses).
• Eliminating hazards (gas leaks, fire, flood, etc.).
• Securing witnesses (identifying all those who can contribute to the investigation).
• Protecting the scene, trying to preserve it in the same condition as left by the offender, especially physical evidence in danger of disappearing. Do not touch anything or allow anyone else to. Do not introduce foreign materials (e.g., cigarette butts, footprints, fibers…).
• Informing the injured party about the imminent arrival of forensic experts and advising them not to manipulate or alter the crime scene. Avoid giving opinions on unknown matters or acting as an expert. Erroneous information about possible tracks, signs, or instruments can lead to frustration and damage the citizen’s perception of police professionalism.
• Maintaining confidentiality about everything seen, heard, or inferred.

B) Forensic Science

Their focus will be on:

• Arriving promptly at the scene to address the needs of injured citizens and ensure the scene remains untampered with.
• Assessing the nature of the event to determine if additional specialized forensic officers are needed.
• Background: Review of complaint proceedings and information from the complainant, witnesses, or acting police officers.
• Comprehensive survey of the site and surroundings, including the route followed by the perpetrator.
• Photographing anything subject to change during the inspection.
• Investigating entry and exit routes of the perpetrator (forced, unforced, scaling).
• Searching, developing, and protecting fingerprints.
• Taking overall, partial, and detailed photographs of the crime scene and the location of revealed tracks.
• Transplanting footprints only when absolutely necessary and with the complainant’s or witnesses’ signed agreement.
• Collecting, storing, and transporting tracks and traces.
• Taking tally sheets of all persons who have manipulated the scene, before or after the crime.
• Drafting a report signed by the complainant or witness, acting officer/s, and sealed.

If the Judicial Authority is present, the inspection will follow their orders for the benefit of the investigation.

C) Investigative Police (Policía Judicial)

Actively participate through:

• Cooperating with forensic technicians, focusing on aspects important for further investigation.
• Centralizing and evaluating collected information.
• Seeking to establish the motive.
• Documenting all activities.

How to Conduct the Visual Inspection

Four key principles:

• Prior information about the incident.
• Meticulous observation of the crime scene.
• Police logic regarding the criminal act.
• A working method that includes peer review of the location, objects, and evidence collection.

Methodology

• Conduct inspections calmly, unhurriedly, and preferably in daylight.
• Never discuss indications or marks in front of strangers or non-expert police officers, as criminal investigations must remain confidential.
• Remember that belief or suspicion is insufficient; evidence is necessary for proof.
• Record all observations during the inspection and write the record with precision.
• Use clear and concise terms in the record.
• Never disregard any detail, no matter how insignificant it may seem, as it could become valuable evidence.

Searching for Tracks and Signs

Guidelines on where to find traces, signs, and other evidence are difficult to establish. Training, experience, observation, deduction, and work method are key for the investigator.

Fingerprint Traces

Fingerprint traces can be visible or latent (invisible).

Visible traces (printed in blood, grease, dust) are easy to locate and do not require reagents. Photography and proper lighting are sufficient.

Latent prints require technical skill and reagents for visualization.

Surfaces Suitable for Retaining Latent Prints

New developers allow visualization on surfaces previously considered inadequate. Suitable surfaces are classified as non-porous and porous.

Non-porous:

• Glass
• Ceramic
• Ivory
• Polished brass, chrome, nickel, or enamel
• Varnished, painted, or lacquered wood
• Painted or lacquered plastic

Physical reagents are used, depending on the surface color. If the object is rough or transferable, it’s collected for laboratory treatment with chemical reagents.

Porous:

• Paper
• Cardboard
• Carton
• Styrofoam
• Others with similar characteristics

These surfaces are treated with chemical reagents (Ninhydrin or DFO) in a laboratory setting.

Table of Developers and Surfaces

Two main brush types:

1. Synthetic or sable brush with very fine hairs to avoid scratching the track. Used with “white lead.” Impregnate the brush with a small amount of reagent and slide it over the suspected latent print. Once visible, clean excess reagent by repeatedly brushing over the ridges. Never use wet reagents or brushes.
2. Magnetic brush: Used for applying magnetic powder and titanium dioxide (white and black). Similar application technique as above. Use a sable brush for cleaning if necessary.

Bounding Fingerprints and Object Identification

Revealed fingerprints must be bounded following these rules:

• Use a pen color matching the reagent (white reagent – white pencil, black reagent – black pencil).
• Bound the entire print, not just identifiable fingers.
• Place metric witnesses on each valuable identification print within the bounded group.
• Identify each object with a sticker containing the case number and address of the affected party.

Transplanting Traces

Transplant only when absolutely necessary (e.g., when photography is impossible or the object cannot be transported).

When transplanting, the injured party or a witness must sign with indelible ink. Note the transplantation in the minutes, stating the number of tracks and their location.

Use clear tape. Place a piece on the track, rub repeatedly, and slowly peel off. Place the tape on a contrasting background (clear plastic or glass is also acceptable).

Checklists

When fingerprints are revealed, obtain tally sheets from everyone who manipulated the objects before or after the crime to eliminate prints of innocent individuals.

Photography

Crime scene photographs must follow an orderly process, from general to specific, providing a complete graphical description and establishing a visual narrative.

Use analog or digital cameras with:

• Wide-angle lens: For general shots of large indoor or outdoor scenes.
• Normal lens: For partial sets and medium-sized details.
• Macro lens: For small details.
• Telephoto lens: For distant scenes inaccessible to the photographer.

Three image footage ranges:

1. General view: Shows the widest possible angle of the crime scene, avoiding people, vehicles, or other extraneous items. Careful camera placement is crucial for a logical view. Take photos before the scene is manipulated.
2. Partial view: Links the general view and detail shots, showing objects in relation to the crime scene.
3. Detail shots: Focus on physical evidence like weapons, fingerprints, crowbars, and damage, establishing their original position. Include a metric witness and identification sticker next to each track, group of tracks, object, or weapon.

Other Non-Fingerprint Evidence

Collect other evidence present at the scene, including:

• Instruments and tools presumably used in the crime.
• Objects whose presence is unjustified (syringes, cigarette butts, etc.).
• Documents (identity cards, letters, newspapers) that may provide information or latent fingerprints.
• Organic stains (blood, semen, saliva) for DNA analysis.
• Inorganic stains (paint, plaster, lime).

Collection and Handling of Biological Samples

Consider these questions when collecting biological samples:

• What is the sample, and why collect it?
• What can be expected from its analysis?
• Is the sample relevant to the case?
• Can it provide data about the incident or the perpetrator’s identity?

If the answers are unclear, do not collect the sample.

Document collected biological samples in the record, describing the evidence, its location, and laboratory conditions. Include detailed photographs of the crime scene and the sample’s location.

Collect samples in the presence of the complainant or a witness, who must sign the collection certificate.

Blood sample collection (most frequent):

• Fresh blood: Collect 5 c/c, store in a labeled tube (cooled if possible), and immediately transfer to the laboratory.
• Bloodstains on absorbent surfaces: Send the entire garment if the stain is small. If the item is large (sofa, mattress), cut out the stained area with a margin of 1-2 centimeters.
• Bloodstains on non-absorbent surfaces: Send the small object directly. If not possible (wall, floor), scrape the stain into a paper envelope.
• Exceptional cases (valuable items): Use a cotton swab moistened with saline or distilled water to rub the stain in a circular motion. Dry swabs at room temperature and place them in individual envelopes, indicating the collection location.

Types of Visual Inspections

Most frequent (and less complex):

• Burglaries
• Theft from establishments
• Vehicle theft

Burglaries

Pay attention to:

• Point of entry (forced door, window), including signs of surveillance.
• General appearance.
• Path followed inside.
• Master bedroom.
• Forced safes, jewelry boxes, etc.

Theft from Establishments

Pay attention to:

• Broken windows.
• Cash register.
• Scattered papers.
• Forced tables, cabinets, and drawers.

Vehicle Theft

Pay attention to:

• Forced doors and windows.
• Mirrors.
• Objects found inside.

Visual Inspection Record

Complete the record in all cases, carefully filling each section:

• Location, date, and time.
• Identification of involved officers and their precincts.
• Crime scene location (full address).
• Type of offense.
• Complainant’s name.
• Eyewitnesses’ names, IDs, and relationship to the complainant.
• Detailed description of the crime scene, including entry and exit points, access methods, and the condition of rooms or vehicle interior. For vehicles, note the starter, steering lock, and mileage.
• Location of revealed fingerprints and the objects they are on.
• List of collected objects and their laboratory destination.
• Whether objects were photographed at the scene or later.
• Number of transplanted tracks and their location.
• Effects collected for laboratory treatment.
• End time, signatures of officers and witnesses, and seal.
• On the back of the record, note tally sheets, modus operandi, and other points of interest.

Key Reminders

The police technical visual inspection is a crucial investigative measure conducted by a forensic science expert.

Its aims are:

• Verify the crime.
• Identify the perpetrator.
• Provide evidence for criminal proceedings.
• Serve as a basis for investigation.

It requires coordination between:

• Forensic science technician (lead).
• Public Security Police.
• Investigative Police.

Principles of visual inspection:

• Prior information.
• Observation.
• Logical work process.
• Methodical approach.

Fingerprints

• Visible.
• Latent.

Common physical developers:

• Lead carbonate.
• White powder.
• Magna Brush (black).

Bound revealed fingerprints with a pencil matching the developer’s color, grouping simultaneous prints.

Include a metric witness and identification sticker with each track or group.

Transplant traces only when necessary, with complainant/witness signatures and documentation in the minutes.

Obtain tally sheets when fingerprints are revealed.

Photography:

• General view.
• Partial view.
• Detail shots.

Biological Sample Collection

• Liquid blood: Collect 5cc, label, refrigerate if possible, and send to the lab.
• Dried blood: Apply filter paper with saline, use swabs, send small objects directly, cut out stains from larger objects.

Types of Inspections

a. Burglary: Entry point, appearance, path inside, master bedroom, forced containers.

b. Theft from establishments: Broken glass, cash register, scattered papers, forced furniture.

c. Vehicle theft: Forced entry points, mirrors, objects inside.

Visual Inspection Report

The report is a carbonless three-part form. One copy is sent to the Judicial Authority. Include all observations, signatures of the officer and complainant/witnesses, and a seal.

Chain of Custody

The chain of custody ensures that evidence collected during the visual inspection is handled lawfully and not tampered with. It maintains the probative value of items so they can be admitted as evidence in court.

Document every step of evidence handling from collection to presentation to the Judicial Authority.

The completed and signed visual inspection report initiates the chain of custody.

Key Reminders

• The chain of custody ensures lawful evidence collection and prevents tampering.
• The visual inspection report initiates the chain of custody.
• The Chain of Custody Record certifies the transfer and handling of evidence.