Introduction to Crime SceneInvestigationILEETA Thanks to Edward E. Hueske University of North Texas Denton, Texas
Duties of First Officer to Scene • Make scene safe for entry • Provide medical attention to injured • Secure scene • Preserve physical evidence • Detain witnesses • Request assistance as needed
Crime Scene Investigation • Team approach will be used • One person must be in charge • Equipment and supplies must be present • Duties must be designated • Search method(s) must be established • Security of scene must be confirmed • Priorities in processing must be established
The Team Approach • Team leader is established prior to arrival Thanks a lot This one’s yours, I had the last one
Duties of Team Leader • Meet with first officer for briefing • Confirm security • Determine legality of search (search warrant) • Call for additional personnel/equipment • Survey scene with first officer • Note fragile evidence/establish priorities • Make notes as to initial observations • Work out action plan with team
Appropriate Crime Scene Attire • Gloves • Shoe covers • Disposable suit • Head gear • Eye protection • Breathing apparatus
Appropriate Crime Scene Behavior • Do not smoke, eat, drink, etc. within the scene • Do not bring equipment into scene and set down within the scene if at all possible • Do not place foreign items down in scene
Documenting the Scene • Photography • Video Taping • Sketching • Diagramming • Note Taking • Report Writing
Scene Searches • Spiral search • Line (strip) search • Grid search • Quadrant (sector)
Vehicle Searches • Photograph as found • Begin with exterior exam/print search • Divide interior into areas • Undercarriage exam (hit & runs) • Inventory and document items as removed • Have items tested as appropriate
Autopsy Evidence • Hair standards • Blood samples – purple-topped tubes • Prints • Fingernail scrapings • GSR test • Sexual assault kit • Recovered bullets, etc.
Collection and Packaging of Evidence • Do not use plastic to package biological evidence • Most evidence is best packaged by placing into a clean sheet of paper, folding, taping and placing in an envelope and sealing • Package evidence separately • Use sharps containers when needed • Obtain required control samples • Maintain a chain of custody record • Use biohazard bag to dispose of contaminated items (gloves, shoe covers, etc.)
Crime Scene Photography • First frame is data card (ea. Roll) • General to specific • Outside to inside • Special documentation (street sign, house number, VIN tag, etc.) Remember: You can’t take too many pictures, but you can take too few!
Crime Scene Photography Scaled Photography • Camera back is in same plane as subject • Fill frame with subject • Include a scale in 1 photo & 1 w/o scale • Use oblique lighting as required • Use a tripod and remote shutter release
Crime Scene Photography Specialized Techniques • Painting with light • Fill-flash • Spray paint “shadowing” • Luminol
Crime Scene Photography Painting with Light • Use for night photography of large outdoor scenes • Use for time exposures of impressions in dust with flashlight
Crime Scene Photography • Use to show background with luminal • Initial exposure of luminal reaction with lens wide open • Manually fire strobe after exposure (use shield on strobe) Fill-Flash
Crime Scene Photography Spray Paint “Shadowing” • Use with available light • Use for impressions in snow • Use for impressions in sand or other soil • Flat black or flat white works best • Spray at an oblique angle
Types of Physical Evidence • Blood, Semen and Saliva • Documents • Drugs • Explosives • Fibers • Fingerprints • Firearms evidence
Types of Physical Evidence • Glass • Hair • Two-dimensional and three-dimensional Impressions • Body fluids and organs • Paint • Petroleum products • Plastic bags (garbage)
Types of Physical Evidence • Polymers & Plastics • Gunpowder Residues • Serial Numbers • Soil and Minerals • Tool Marks • Vehicle Lamp Bulbs • Wood & Vegetative Matter
The Goal of Physical Evidence • Positive Identification • Association • Circumstantial
Comparative Analysis • Known to Unknown or “Q” to “K” • Physical comparison (physical properties/jig-saw puzzle fit) • Chemical comparison • Class characteristics • Individual characteristics
Range of Conclusions • Identification (common origin) • Same source or a similar source (either/or) • Member of same class (cannot be excluded) • Exclusion (different origin)
Ignorance is Bliss • What is a class characteristic? • What is and individual characteristic? Knowledge is the key
Evidence and Probability • Most of the time a mathematical expression is inappropriate (Highly probable vs. highly improbable) • Some situations do lend themselves to a mathematical expression of probability (DNA is a prime example)
Probability and Statistics • Coin toss – 1 in 2 probability • Roll of a die – 1 in 6 probability • Roll of a pair of dice to yield “snake eyes” – 1/6 x 1/6 = 1/36 (1 in 36 probability) • There are 4 aces in a deck of 52 cards, what is the probability of drawing an ace at random? • What is the probability of drawing a king of any suit? • What is the probability of drawing an ace and a king with 2 draws from a full deck?
Probability and Statistics • DNA analysis is based on the presence of certain fragments within the DNA molecule • For each fragment there is a certain frequency (probability of occurrence) within a particular ethnic group of a population • If 7 different fragments are identified as being present, how is the probability of that occurring in someone else calculated?
Probability and Statistics • A vehicle with 4 different brands of tires leaves all 4 different tread patterns at a crime scene. A suspect is arrested with a car with 4 different tires, each similar to one of the crime scene impressions. • Is it possible to calculate the probability of finding the same situation on another car? • What considerations are involved?
Negative Evidence • “Absence of Evidence is not evidence of absence” • Nevertheless, what is not present can provide useful information as to how a crime may have been committed • Ex: No shoe impressions on driver side of vehicle but shoe impressions leaving the passenger side • Faulty reasoning: no blood in trunk, therefore victim was not transported in trunk.
Crime Scene Reconstruction • Who? • What? • When? • Where? • How? • Why?
Crime Scene Reconstruction • On-scene • Off-scene • Re-enactment: • Live actors • Mannequins