Solving the crime will depend on piecing together the evidence to form a picture of what happened at the crime scene.
*Physical Evidence-encompasses any & all objects that can establish that a crime has been committed or can link a crime & its victim or its perpetrator. Evidence can be classified as direct or circumstantial evidence.
*Direct evidenceevidence that (if true) proves an alleged fact; includes first hand observations such as eyewitness accounts. Confessions are also considered direct evidence. Also police dash videos *Circumstantial evidence is indirect evidence that can be used to imply a fact but that does not directly prove it; but circumstantial evidence at a crime scene may provide a link between the crime scene and the suspect. Circumstantial evidence can be either physical or biological in nature.
Physical evidence includes impressions such as
and shell casings.
Biological evidence includes
Evidence can also be divided into class evidence & individual evidence. *Class evidence narrows an identity to a group of persons or things. Ex blood type *Individual evidence narrows an identity to a single person or thing.
Class Evidence Examples
Single layered paint
Evidence that contain Individualizing Characteristics
Shoeprints (wear patterns)
Glass fragments that can be matched
Whenever two people come in contact with each other, a physical transfer occurs. Hair, skin, clothing fibers, pollen, glass fragments, any number of different types of material can be transferred from one person to another. These transferred materials constitute what is called trace evidence. *Trace evidencesmall but measurable amounts of physical or biological material found at a crime scene.
The first person to note this condition was Dr. Edmond Locard, director of the world’s 1st forensic laboratory in Lyons, France. Locard’s Exchange Principlestates that when a person comes into contact with an object or another person, a cross transfer of physical evidence can occur. The exchanged materials indicate the two objects were in contact. The second part of Locard’s Principle states that the intensity, duration and nature of the materials in contact determine the extent of the transfer.
The Seven S’s of Crime-Scene Investigation Securing the scene Separating the witnesses Scanning the scene Seeing the scene Sketching the scene Searching for evidence Securing & Collecting evidence
The 1st priority at the crime scene is to preserve life & help any living victims. The 2nd priority is to detain & question any suspects & remove them from the scene. Potential witnesses should be detained, separateddone to avoid witnesses working together to create a story (collusion) & questioned. Police must secure the crime scene to prevent traffic through the area that may destroy or contaminate evidence. In order to be useful, evidence at a crime scene must be preserved & recorded. Good record keeping is essential
Secure & Isolate the Crime Scene Destruction or altering of P.E. can occur when a crime scene is not properly secured & documented. Investigators only have a limited amount of time to work a crime site in its untouched state. The opportunity to record the CS in its untouched state must not be lost.Responsibilities of 1st Officer arriving:1. obtain medical assistance for anyone in need2. arrest any perpetrators3. exclude all unauthorized personnel4. isolate the area
Once the C.S. has been secured the lead investigator will:1. determine the boundaries of the C.S.2. establish the perp’s path of entry & exit3. proceed w/ an initial walk-through4. develop a strategy for examining and documenting the entire C.S.5. Determination of primary & possible secondary crime scenes6. Obvious evidence documented & photographed.
*Primary crime scenethe location where the crime took place *Secondary crime scene a location other than the primary crime scene, but that is in some way related to the crime, where evidence is found
Record the Scenethe time a C.S. remains untouched is limited; therefore timely recording of the C.S. is essential for the investigation and any subsequent trialsUse of Photography, sketches, & notes are the 3 methods for crime-scene recording.
Photography an unaltered C.S. is most important; objects must NOT be removed until they have been photographed from all angles. if any object is moved or removed from the C.S. it should be noted – under NO circumstance should it be reintroduced C.S. photos should include not only the immediate scene but also: all relevant angles adjacent areas close-ups of victim’s relative position in the scene and any injuries possible weapons the area under the body evidence is photographed as it is found and if size is significant, a point of reference should be included in the photo New Technology digital photos allow near three-dimensional panoramic views of the crime scene videotaping the C.S. is rising in popularity – the investigator must narrate as he/she records the scene
"Golden Rule" of Crime Scene Investigation/Management "Never touch, change, or alter anything until it has been documented, identified, measured, and photographed . . . when a body or article has been moved, it can never be restored to its original position."
Sketches Once photos have been taken, the crime-scene investigator sketches the scene * Rough Sketcha draft representation of all essential info & measurements at a crime scene. This sketch is drawn at the crime scene. It shows dimensions & location of objects. On the sketch, North should be labeled. Objects are located in the sketch by distance measurements from 2 fixed points. All measurements are made w/ a tape measure. The simplest way to designate an item is to assign it a # or letter. A legendmust be placed below the sketch. *Finished Sketcha precise rendering of the crime scene, drawn to scale.
Notetaking is a constant activity when processing C.S. and must include:
detailed written descriptions of C.S. w/ locations of P.E. including also:
time of discovery
who found it
who packaged and marked it
disposition of item after being collected
must be detailed enough to refresh one’s memory months years after processing
tape or video recording is advantageous but at some point it must be transcribed
Searching for Evidence The search pattern selected at a crime scene depends on the size & locale of the scene & the # of collectors participating in the search. Typical examples of crime scene search patterns are: 1.Grid 2. Linear 3. Quadrant or Zone 4. Spiral
Crime Scene Search Patterns
SPIRAL GRID LINEAR
Securing & Collecting Evidence 1. Evidence can be massive to microscopic 2. may only be detected in a crime lab ex. traces of blood on clothing, hair and fibers from vacuum sweeps 3. it is sometimes necessary to confiscate clothing from victim and perp Critical areas should be vacuumed; sweepings from different areas must be kept separate 5. finger nail scrapings must also be taken from suspects and victims
Securing & Collecting Evidence 6. Trace evidence should be left on object unless it is attached to a large object; remove w/ forceps 7. Bloodstains
scraped if dry
transferred to moistened swab
cut out the area of object
8. Each item must be kept separately
Securing & Collecting Evidence All evidence needs to be properly packaged, sealed and labeled. The evidence log should contain all pertinent information including:
Item inventory #
Description of the evidence
Name of suspect
Name of victim
Date & time of recovery
Signature of person recovering the evidence
Signature of any witnesses present
Obtaining Standard/Reference Samples 1. Collect evidence from suspects and victims that are similar to the P.E. collected @ the scene paint from vehicles hair or blood 2. buccal swab 3. substrate control
Reference Samples * control samplemust be obtained from victim for purposes of exclusion *standard/reference samplephysical evidence whose origin is known, that can be compared to crime scene evidence. The presence of reference samples greatly facilitates the work of the forensic scientist. Ex: blood or hair from possible suspects to be compared to crime scene evidence. * Buccal swabswab of inner portion of cheek, performed to collect cells for use in determining DNA profiles * Substrate controluncontaminated surface material close to an area where phys evidence has been deposited; used to ensure that the surface on which a sample has been deposited does not interfere w/ lab tests
Packaging the Evidence
Evidence is placed in a paper bindle. The size of the bindle depends depends on the size of the evidence.
Entire object should be sent to the lab.
Each different item must be placed in separate containers. Packaging evidence separately prevents cross contamination.
small amts of trace evidence can be conveniently packaged in a carefully folded paperdruggist fold: folding one end of the paper over 1/3, then folding the other end (1/3) over that, & the repeating the process from the ther 2 sides. After the paper is folded, the outside 2 edges r tucked into each other to produce a closed container.
Manila envelopes or sealable plastic bags can be used for some evidence.
Wet evidence should NEVER be packaged in plastic containers while wet.
Bloodstained materials should NOT be stored in airtight containers b/c accumulation of moisture may encourage the growth of mold; in these instances wrapping paper, manila envelopes or brown paper bags are used.
All items of clothing must be air dried & place in individual separate bags.
Charred debris recovered from a fire must be sealed in airtight containers to prevent evaporation of volatile petroleum residue. (new paint cans or tightly sealed jars)
Chain of Custody An evidence log and a chain of custody document must be attached to every evidence container. *Chain of Custodythe documented and unbroken transfer of evidence; list of all people who came into possession of an item of evidence (continuity of possession) Maintaining chain of custody is essential.
Chain of Custody · every person who handles the evidence must be accouted for · all items must be carefully packaged & marked upon their retrieval at the scene. · Record to show collector’s initials, location of evidence, & date of collection.
Seal the evidence & the collector’s signature is written across the sealed edge.
When the package is reopened at the lab it is opened at a location other than the sealed edge. Every time opened: new seal, new signature, place in new evidence bag.
Crime Scene Reconstruction * CRIME SCENE RECONSTRUCTIONinvolves forming a hypothesis of the sequence of events from before the crime was committed through its commission; It’s a method used to support a likely sequence of events at a crime scene by observing & evaluating physical evidence & statements made by those involved. Reconstruction is a team effort that involves putting together many different pieces of a puzzle. The collection & documentation of physical evidence is the foundation of a reconstruction. A reconstruction supports a likely sequence of events by observing & evaluating physical evidence & statements made by those involved. The investigator captures the nature of the scene on an initial walk through. Using physical evidence he can hypothesize about what occurred, where it occurred & when it occurred.