What is Forensic Science?
The application of all scientific disciplines 2 matters of law
AKA criminalistics
Criminalist
scientist who applies the principles of biology, physics, and chemistry 2 evidence analysis and is also trained in crime scene investigation and reconstruction
Forensic
general term that may apply 2 any # of sciences
potentially includes ALL fields of science
(open to debate)
The Cornerstone of Modern Forensic Science: The Locard Exchange Principle
Dr. Edmond Locard (1877-1966)
The exchange or transfer of materials when 2 or more items come into contact
"every contact leaves a trace
The Forensic Laboratory
Analyzing physical evidence
Involved in all aspects of recognition, collection, and preservation of evidence
1st Forensic Science Lab: 1923 August Vollmer/ L.A police dept (government associated)
1st Private F.S Lab: 1929 Chicago
1932 FBI- national lab
Types of Forensic Labs (Government Sponsored)
1) Government-sponsored:
-City
-County
-Regional
-State
-Federal
Association with law enforcement vital 2 government lab operations
Should never influence outcome of investigation
(No jumping to conclusions or implying guilt in casework)
Types of Forensic Labs (Private Labs)
2) Available 2 law enforcement or individual defendants
Adversarial judicial system makes private labs necessary (Defendants can challenge witnesses)
Primarily involved in retesting evidence tested by government lab
Requirements for Forensic Labs (Quality Assurance Program)
Designed to ensure results are scientifically valid and reliable
Must be strictly maintained
May include:
-Education requirements for staff
-Peer review of results and reports
-Case file documentation
-Testimony audits
-Evidence handling procedures
-Lab S
Requirements for Forensic Labs (Proficiency Testing)
Simulated forensic cases evaluated by criminalist as if it is the real thing
May be internally generated or provided through outside testing agency
Requirements for Forensic Labs (Accreditation)
Lasts for 5 years
American Society of Crime Laboratory Directors (ASCLD)
Endorsement of lab's policies and procedures
Must demonstrate proficiency
Common Lab Sections
1) Forensic Biology: Biological Evidence
-Identification and individualization of human tissues
2) Serology: the study of bodily fluids including blood groups and sometimes blood spatter, semen, urine and saliva
-DNA analysis
3) Trace Evidence: microscopi
Common Lab Sections Continued
4) Fingerprint Evidence: Latent print development, identification
5) Impression Evidence: Footwear and tire impressions
May provide identification of footwear or tire
6) Reconstruction Evidence: provides information about events preceding, during, and aft
Common Lab Sections Continued...
9) Individual Characteristics: characteristics that associate a particular individual or object with the commission of a crime
-"match"
10) Firearm and Tool Mark Evidence: Fired bullets, cartridge casings, shotgun shells, miscellaneous tool marks
11) Ques
The Forensic Examiner
BA in natural science required
-Chemistry
-Biology
-Physics
-Forensic Science
Entry-level positions available w/ BA
-most career skills gained on the job
Some specializations require advanced degrees
Investigator
Review scene reports
Diagrams and photos
Collected evidence
Witness/suspect statements
Police reports
Provide investigative leads through scientific evaluation of physical evidence and scene reconstruction
Educator
Report results and conclusions of scientific evaluations
Provide expert testimony
Student
Continuing education
On-the-job training
Research
Forensic Impression Evidence: Footwear Analysis
Types of footwear impressions
1) 3-dimensional: remain after a shoe has permanently deformed a surface
Commonly found on exterior surfaces:
-Soil -Sand -Clay -Snow
2) Plastic: impressions made in soft, malleable material
-Snow -Mud -Wet Sand -Soft tar -Wet cement
3) 2-dimensional: rem
Shoe Prints as Evidence
Shoeprint impressions= class evidence
-Identify type (shape)
-Identify manufacturer (design)
-Identify size of shoe
Elimination of Footwear
Confirmable differences in class characteristics
Changes in or absence of individual characteristics NOT used for elimination
May provide exculpatory evidence
Determination of shoe size
Determination of shoe brand/ designer
-FBI footwear database-thousand
Wear Patterns: Individual Evidence
People routinely walk over same types of surfaces during normal course of activities
-Types of surfaces vary from person to person
Involves degree and position
-Ranges from new 2 extremely worn
Manufacturing Defect
Unintended damage, defects, or flaws in footwear outsole that occur during manufacturing
*May result in class or individual traits
-depends on cause
Randomly Acquired Characteristics (aka, accidental characteristics= individual evidence)
Position, orientation, size, and shape contribute to uniqueness of impression evidence
Everyone leaves a unique shoe print
Identification of Footwear
Suspect's shoe may be positively identified
-individualization
Demonstrates suspect's presence at scene
Problem:
-Wear pattern changes over time
-Individualizing characteristics become altered or lost
*Positive match impossible
Participation in the Crime
Impressions left on objects moved during commission of crime
Location of Impressions
Points of entry and exit
Trace movement of suspect through scene
May provide investigative leads or discovery of physical evidence
Confirm or Refute Suspect's alibi
Presence or absence of suspect
Location and movement of suspect in crime scene
Minimum Number of Perpetrators
Discovery of more than 1 suspect footwear impression
Absence of more than 1 suspect impression
Linking Crime Scenes
Same footwear impressions found @ multiple scenes
Same individual involved
Useful in repetitive crimes
-burglaries
Shoeprints as Evidence
Gait characteristics:
Primarily a medical evaluation 4 problem walking
Measure:
-step length
-stride
-step width
Changes w/ speed and surface type (also diff. shoe types)
Tracking
Following path of a person by observing evidence created as he/she moves over various surfaces
-illegal immigrants
-missing children
Location of Footwear Impressions
Slow, visual search of scene
Dim lights, search again w/ high intensity light source
-oblique angles
Remember to examine any items that may have been stepped on
Documentation of Footwear Impressions
Notes
-location
-direction of prints
-description
Photos
-Examination quality photos
-35 mm or larger w/ manual focus required
-Ruler or scale in every photo
-Oblique lighting from 3 sides
Recovery of Footwear Impressions (2-dimensional print techniques)
Improves impression visibility and detail
Transferred to background providing better contrast
Allows removal of print from scene to lab
1) Electrostatic lifting (ESC)
-high-voltage power source 2 create static electrical charge
-results in transfer of dry
3-D Print Techniques for Recovery
1) Dental Stone
-Viscous gypsum-based material
-Sets harder and faster than plaster
-Higher compressive strength
-1st choice for casting all 3-D impressions
2) Plaster, Silicone
-May be used for prints in snow or other special cases
3) Sulfur
Enhancement Methods
Techniques used to make latent impressions visible
May also be used to increase contrast w/ underlying surfaces or otherwise improve visualization of detail
Forensic Photographic Methods
Nondestructive; excellent option for 1st attempt @ enhancement
Oblique lighting
High contrast methods
Ultraviolet
Infrared
Alternative light sources
Physical Methods for Enhancement
Powders
Indentations on paper items
Chemical Methods for Enhancement
Bloody Prints:
-Amido Black powder (bluish color)
-Luminol (bluish)
-Fuschin acid (reddish protein stain)
-Leucocrystal Violet (LCV)
Simple residue prints:
-Physical Developer (PD)
*silver-based liquid reagent
*reacts w/lipids, fats, oils, and waxes
*good
Digital Methods for Enhancement
Computer software applications
Increase contrast and brightness
Superimposition
Generally improve visualization of impressions
Enhancement NOT Alteration
Exemplars
Comparison of known shoe prints 2 suspect impressions for purpose of elimination
-impressions of all scene personnel
-victim(s)
-suspect(s)
Elimination Footwear
Footwear of scene personnel or other innocent persons who could have left recovered impressions
Must account for all impressions recovered from scene
-Unlikely that perpetrator's shoe design is known during processing of scene
Footwear From Suspects
Minutes-2 hours after commission of crime:
-perpetrator likely wearing same shoes worn @ crime scene
2 hours-days after commission of crime:
-must seize and analyze all shoes owned by suspect
Test Impression
Impression made using known shoe as a standard
-Inks
-Fingerprint powders
-Chemical papers (ink less methods)
-Casting materials (silicon)
-Foam impression blocks
Goal: highly detailed, repetitive samples of class and individual characteristics of each sh
Examination Process
Comparison of full and partial crime scene impressions w/ known shoes
Methods:
-side-by-side comparison
-superimposition
-magnification
-lighting
-exemplar comparison
Examiner's opinion based on:
1) Design
-If clearly different, then eliminated
2) Physical size and shape
-Design: size combination represents small fraction of 1% of entire shoe population
3) Wear
-Position of wear- area(s) on sole that reflect visible wear
-Degree of wear- extent to
Positive Identification
(Highest level of opinion an examiner can give)
Crime scene impression and known shoe sole share sufficient individual identifying characteristics
-No minimum number required
Conclusion that a particular shoe, and no other shoe, made crime scene impressio
Exclusion (elimination)
Examiner's opinion that particular known footwear was not the source of and did not make the impression
Insufficient Detail
Finding that availability of features falls short of allowing confirmation of certain class or randomly acquired characteristics
Forensic Impression Evidence: Tire Evidence and Analysis
(can give same range of opinions as a shoe print expert*: Tire Impressions
Tire Impressions:
-reflect tread design and dimensional features of individual tires
Tire Footprint
Contact area of a tire tread against a flat surface while under load (aka, contact patch)
Full Circumference Tire Impression
Impression representing a full rotation of a tire under load
Tire Tracks
Relative dimensions between 2 or more tires of vehicle
Track Width
Distance between the center points of the tires from one side of the vehicle to the other
Wheelbase
Distance from center of front wheel to that of the rear wheel in a motor vehicle, usually expressed in inches
Turning Diameter
...
Types of Tires
1) Original Equipment (OE) Tires
-sold as equipment on new vehicles
-high volume (thousands of the same tires)
2) Replacement Tires
-Purchased 2 replace worn or damaged tires
3) Retread Tires
-Tire carcass 2 which new tread rubber is added to produce a re
Parts of a tire
Liner (keeps air inside tire), rim cushion, belts, sidewall rubber, plys, filters- 4 spacing, Bead (hoops of steel wire that hold tire to rim), veneer
Tire Construction (drawings in NB)
1) Radial Construction
-Plies run straight across tire; 90 degrees 2 center line of tread
2) Bias Construction
-Plies run @ oblique angle (bias) across tire
3) Belted Construction
-Belts beneath tread surface
(metal-steel) adds strength to tire
Tread Rubber
Thick layer of rubber w/out design
Applied last 2 outer surface of carcass
Green Tire
Contains no tread design or sidewall information
Tread Nomenclature
1) Design Elements: a single raised rubber design on tire
2) Ribs or Tread Blocks: design elements running around circumference of tire
-Center Rib: runs circumferentially and is evenly centered w/in the tread design
3) Grooves: channels running around th
Sidewall Information
Label Side:
-Outer Wall
-Tire brand and style
-Size
-Raised white lettering or whitewall
Serial Side:
-Normally not visible
-Tire brand and style
-Size of tire
-DOT #
P215/65R15 89H
P= passenger tire
215= width of tire in mm
65=ratio of height to width (aspect ratio) small number= wide/ short tire that increases stability, high number= less wide/ longer w/ decreased stability
R= radial
15= diameter of wheel in in.
89H= load index and
Traction
A tire's ability to stop on wet concrete- A grading= good
Treadwear
the higher the number the longer it will last
DOT #
Department of Transportation:
-Begins with DOT
-Followed by 2 digits (letters or letter and #)= plant code
-Final 3-4 digits (#'s)= date of manufacture
*usually found in indented panel
Old code= 089, 08= week 9= year (PROBLEM!)
New code= 4901, 49=week, 01
Retread Tires
Most commonly used on large fleet vehicles
Two methods of production:
1) MoldCure: blank strips of raw rubber applied to tire carcass and placed into mold
2) Precure: bonding of rubber pre molded w/ tread design to carcass
Dept. of Transportation # listed
Tire References and Databases
1) Tread Design Guide:
-Photos of most tire designs
2) Who Makes It and Where:
-List of manufacturers codes and locations
-Both guides available on CD-ROM
Recovery of Tire Evidence
1) General Scene Photos:
-Multiple angles
-Photo log
2) Detailed Notes
-# of tracks
-Relationship to each other and surroundings
-Track width
-Direction of travel
3) Diagrams
4) Exam quality photos of impressions
-fill the frame - 90 degrees -scale -obliq
Casting Tire Impressions
Provides more info than photos alone:
-3-D aspects of impression
*Tread depth: vertical measurement between top of tread and deepest groove
- Contours
-Uneven qualities of depth
Deep impressions may retain wear bar impression and or sidewall detail
-Fill
Reference Print
Exemplar
Used for comparison
Tire Impression Analysis
1) Tread Design
2) Tread Dimension & Noise Treatment
3) Wear Features (blending between class and individual)
4) Random Individual Characteristics
*Schallamach Pattern (aka, feathering): microscopic patterns that develop as ridges on rubber from repeated
Forensic Impression Evidence: Tool Marks
Tool Marks: any impression, cut, gouge, or abrasion caused by a tool coming into contact w/ another object
-Impressions into softer surface
-Abrasions by tools cutting or sliding against another object (harder surfaces)
Classification of Tool Marks
1) Compression/ Indentation Marks: occur when a tool is pressed into soft material
-tend to show the outline of the working surface of the tool
-class characteristics visible:
*size
*shape
Difficult 2 visualize individual characteristics
-rare
2) Sliding
Classification of Tool Marks Cont...
3) Cutting Marks: left by tools as they slice through materials
-Lines and striations across cut surface
-Many cutting tools ground or sharpened by hand...
*resulting striation pattern may be unique to particular tool
-Best materials for comparing cut sur
Preserving Tool Impressions
Document- Notes, Photos, Sketches
Remove for lab analysis
-if moveable, take entire item to lab
- if immoveable, cast impressions
*Rubberized silicon is most likely used
* Retains minute microscopic details
Never place suspect tool into contact w/ impress
Laboratory Examination
Must examine questioned tool marks and any tools submitted for examination
Elimination of suspect tools
Preparation of test marks for microscopic examination
-May use soft test material or same type of material found @ scene
-Marks must be made in same ma
Microscopic Comparisons
Comparison Microscope: device used to observe side-by-side specimens
Consists of 2 microscopes connected to an optical bridge
Results in a split view window
Used in forensic sciences to compare microscopic patterns and identify or deny their common origin