Science and Technology in Criminal Investigations: A Comprehensive Guide
The Crucial Role of Science and Technology in Criminal Investigations
Presumptive Tests: Field Science for Patrol Officers
Purpose: Preliminary scientific testing performed in the field by patrol officers who are not trained criminalists or organic chemists.
Function: To quickly determine if a substance is likely illicit (e.g., drugs) or identify a substance (e.g., blood).
Process: Officers carry pre-packaged plastic vials. A small substance sample is placed in the vial, which is then cracked and shaken. A color change indicates a positive presumptive result.
Example: Narcotics: A white crystalline substance turning blue indicates meth or cocaine, leading to an arrest.
Example: Blood: Similar presumptive tests exist for identifying blood at a scene.
Case Example: Montecito Drug Dealers:
Cocaine was discovered in unusual long brick shapes, smuggled in vehicle frames, leading to a major drug bust.
During the search, clothing with dried reddish-brown stains was found.
Initial excitement that it might be blood evidence from an unsolved homicide (Louie Warner case, Joe Dominguez as suspect) was tempered.
Major crimes/homicide personnel conducted a presumptive test on the stains, determining it was paint, not blood. This allowed the investigation to pivot.
The Historical Evolution of Forensic Science
Early Applications of Evidence
Julius Caesar Era: Early use of evidence to determine causes of death.
Ancient Eastern Cultures: Recognized the uniqueness of fingerprints and used them in business dealings.
Shift from Unreliable Methods
Historically, methods like harsh interrogation and torture were used to extract truth.
This approach proved highly unreliable, as individuals would often confess to anything to stop the pain, regardless of truth.
The Scientific Era (Beginning Late th / Early th Century)
Foundation: Marked by the systematic application of scientific principles to criminal law.
First Crime Lab: Established by Chief August Vollmer at the LAPD in Southern California, a surprising fact to many who might guess the FBI or NYPD.
Key Scientific Applications:
Toxicology: Analysis of bodily fluids for various substances.
Ballistics: Realization that every gun barrel leaves unique identification marks on bullets passing through it, requiring dedicated laboratory analysis.
The Technological Era (Beginning Circa s)
Advancement: Significant sophistication in evidence detection and collection capabilities.
Automated Fingerprint Identification System (AFIS):
Legacy Method: Manual comparison of fingerprints by experts (e.g., Bob Spinner) often requiring identification of points of similarity between a print from a crime scene and a known suspect print from booking records.
Modern Method: Digitized system where computers can rapidly compare and match prints.
Process: Fingerprints (from arrests, e.g., at county jail or metropolitan detention centers for federal cases) and DNA swabs are routinely collected and digitized.
Operational Use: Patrol officers lift prints at crime scenes, upload them to AFIS, which can identify potential matches. Human confirmation by a criminalist is still required but computer matches are almost always correct.
Case Example: A print lifted at a residential burglary entered into AFIS matched a person arrested three years prior by Oxnard PD in Ventura County, leading to suspect identification.
Combined DNA Index System (CODIS):
Function: A national database for DNA profiles.
Process: DNA profiles from arrested and booked individuals are uploaded to CODIS.
Cold Case Matching: A DNA profile from an unsolved crime can be uploaded. If no immediate match, it means the individual has not been previously arrested and booked.
Case Example: Isla Vista Sexual Assault:
A severely intoxicated victim was violently sexually assaulted by three individuals behind eucalyptus trees near UCSB.
Usable DNA evidence was left at the scene, yielding a DNA profile, but no identity was known.
The profile was uploaded to CODIS, initially without a match.
Later, a suspect, Mister Chen, was arrested for selling weed in Northern California.
Upon booking into county jail, his DNA was collected and uploaded to CODIS.
The system generated an immediate match to the Isla Vista sexual assault case, leading to Chen's conviction (receiving a year sentence for a first offense). This highlights CODIS's role in connecting crimes to individuals through subsequent arrests.
Crime Scene Management and Evidence Collection
Roles and Responsibilities at a Crime Scene
Patrol Officer: First responder, main job is protecting the scene.
Actions: Sets up crime scene tape, establishes a single entrance/exit, prevents unauthorized personnel (looky-loos) from entering, ensures no evidence is transferred in or out, and identifies witnesses/suspects.
Crime Scene Technicians (CSTs):
Staffing: Usually non-sworn (civilian) personnel.
Tasks: Photograph evidence, collect potential evidence, and sometimes perform preliminary field tests.
Job Outlook: Very difficult jobs to obtain due to low numbers and high demand (e.g., Santa Barbara County has only a handful of CSTs across multiple agencies, paying about half of a detective's salary).
Detectives: Generally coordinate and formulate investigation plans.
Evidence Collection: Detectives typically do not collect evidence unless it's a non-major case.
Critical Crime Scene Procedures
Securing the Scene: Paramount to protect evidence from damage, contamination, or removal. This often involves extensive crime scene tape.
Crime Scene Walk-Through: Conducted as few times as possible by one person, often with a video camera.
Purpose: To gain a preliminary view of the scene, identify potential evidence, and plan the collection strategy.
Principle: Minimizes contamination, adhering to Locard's Exchange Principle (every contact leaves a trace).
Sketching and Mapping the Scene: Essential alongside photography.
Benefits: Captures spatial relationships, relative positions, and items that might be obscured or out of frame in photos (e.g., the Ron Goldman case where his body was not visible in photos but clear in the sketch of the OJ Simpson crime scene).
Application: Helps witnesses recall events, assists investigators in understanding the scene, and provides clear visual aids for juries in court.
Methods for Sketching:
Rectangular Coordinates: Measuring an item's position (e.g., keys on the floor) by taking two perpendicular measurements from two known, fixed walls (e.g., ft inches from one wall, ft inches from another).
Triangulation: Measuring an item's position from two non-changing, known points (e.g., two corners of a room), using the points of intersection from the measurements.
Evidence Collection Techniques: Organized search patterns are crucial to ensure nothing is missed.
Strip Technique: Multiple investigators walk shoulder-to-shoulder in a straight line, sweeping the area for evidence.
Grid Technique: Combines the strip technique, followed by another pass perpendicular to the first, creating a grid for thorough coverage. This is highly effective.
Spiral Technique: Starting at the center and spiraling outwards, or vice versa; effective for a single investigator or smaller areas.
Case Example: Katrina Nichols Homicide: Sheriff's department failed to use an organized technique at a body dump site on East Camino Cielo. During the jury trial, the jury visited the scene and found a piece of clothing (crime scene evidence) that had been missed, highlighting the consequences of sloppy work.
Determining Crime Scene Boundary Size:
Principle: It is much easier to make a crime scene smaller than to expand it once it's been contaminated.
Strategy: Default to making the crime scene larger than initially seems necessary. Consider potential paths of individuals involved.
Balance: Weigh the need for thorough investigation against the disruption caused by shutting down large areas (e.g., an entire building for a homicide). Initial broad containment allows for later reduction as more is known.
Types of Physical Evidence and Documentation
Definition: In law enforcement,
Presumptive Tests: Field Science for Patrol Officers
Purpose: Quick, preliminary field tests by patrol officers to identify likely illicit substances (e.g., drugs) or blood.
Process: Substance mixed in a vial; color change indicates a positive result.
Example: Montecito case where a presumptive test on clothing stains determined it was paint, not blood, redirecting the investigation.
The Historical Evolution of Forensic Science
Early Applications of Evidence
Early use of evidence (Julius Caesar) and fingerprint recognition (Ancient Eastern Cultures).
Shift from Unreliable Methods
Replaced highly unreliable methods like torture with scientific approaches.
The Scientific Era (Late th / Early th Century)
Systematic application of science to law.
First Crime Lab: Established by Chief August Vollmer at the LAPD.
Key Scientific Applications: Toxicology, Ballistics (unique gun barrel marks).
The Technological Era (Circa s)
Automated Fingerprint Identification System (AFIS):
Replaced manual comparison; computers rapidly match digitized fingerprints from crime scenes to booking records. Human confirmation is still required.
Case Example: AFIS matched a print from a residential burglary to a suspect arrested three years prior.
Combined DNA Index System (CODIS):
National database for DNA profiles from arrested individuals.
Enables cold case matching, identifying suspects years later through subsequent arrests.
Case Example: Mister Chen, arrested for a minor offense, was linked via CODIS to an unsolved Isla Vista sexual assault, leading to his conviction.
Crime Scene Management and Evidence Collection
Roles and Responsibilities at a Crime Scene
Patrol Officer: First responder, primary role is protecting the scene (securing boundaries, preventing contamination).
Crime Scene Technicians (CSTs): Non-sworn personnel who photograph, collect evidence, and sometimes perform field tests.
Detectives: Coordinate investigations, typically do not collect evidence themselves in major cases.
Critical Crime Scene Procedures
Securing the Scene: Crucial to protect evidence; involves crime scene tape and restricted access.
Crime Scene Walk-Through: Minimal, single-person overview to plan strategy, adhering to Locard's Exchange Principle.
Sketching and Mapping the Scene: Complements photography, capturing spatial relationships for investigators and juries. Methods include Rectangular Coordinates and Triangulation.
Evidence Collection Techniques: Organized search patterns are vital:
Strip Technique: Linear sweep.
Grid Technique: Two perpendicular strip searches, highly effective.
Spiral Technique: For single investigators or small areas.
Case Example: Katrina Nichols homicide highlighted consequences of disorganized searches (missed evidence).
Determining Crime Scene Boundary Size: Always start larger than necessary; easier to reduce than expand after contamination.
Types of Physical Evidence and Documentation
Definition: In law enforcement, physical evidence refers to any material object that can link a suspect to a victim or crime scene.