Forensics: IntroductionGuided Notes

Impressions

SFS4 Students will evaluate the role of ballistics, tool marks and evidence of arson in forensic investigation.

c. Recognize the forensic significance of tool marks, footwear and tire impressions in an investigation.

SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science.

b. Distinguish and categorize physical and trace evidence (e.g. ballistics, drugs, fibers, fingerprints, glass,

hair, metal, lip prints, soil, and toxins).

Learning Targets: I can

oDistinguish between patent, latent, and plastic impressions

oDescribe how to make foot, shoe, and tire impressions

oUse track width and wheel base information to identify vehicles

oPrepare dental impressions and match them with bite marks

Impressions

Patent impressions –

Latent impressions –

Plastic impressions –

Tool marks

  • Any impression, scratch, or abrasion made when ______between a tool and an object.
  • It is the presence of any minute ______ on a tool that imparts individuality to that tool.
  • The ______and ______of such imperfections are further modified by ______and ______during the life of the tool.
  • The comparison microscope is used to compare crime-scene tool marks with test impressions made with the suspect tool.
  • Observation of ______on tools to compare to marks made at the crime scene can help link a particular tool to a crime scene and possibly a suspect.
  • When practical, the entire ______, or the part of the object bearing the tool mark, should be submitted to the crime laboratory for ______.
  • Under no circumstances must the crime scene investigator attempt to fit the suspect tool into the ______.
  • Any contact between the ______and the ______may alter the mark and will, at the very least, raise serious questions about the integrity of the evidence.
  • Instead, a ______or putty ______should be used to mold a pattern of the weapon.
  • Most common types of tool marks include:
  • Abrasion marks –
  • Cutting marks
  • Indentation marks –

Other impressions

  • Impressions of other kinds, such as ______, ______, or ______ impressions, may be important evidence.
  • Before any impression is moved or otherwise handled, it must be ______(with a scale included) to show all of the observable details of the impression.
  • Tire and ______prints can be preserved by ______them in plaster.
  • Fabric ______can be made in a variety of ways.
  • If the impression is on a readily recoverable item, such as ______,______, or ______, the evidence is transported intact to the laboratory.
  • If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to ______a ______.
  • When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by ______and ______.
  • In areas where a bloody footwear impression is very faint, or where the subject has tracked through blood leaving a trail of bloody impressions, ______ can visualize latent or nearly invisible blood impressions.

Points of Comparison

  • A sufficient number of ______ or the uniqueness of such points will support a finding that both the questioned and test impressions originated from one, and only one, source.
  • New computer software and web sites may be able to assist in making shoe print and tire impression comparisons.
  • Also, ______ impressions on skin and foodstuffs have proven to be important ______in a number of homicide and rape cases.

Shoe Impressions

oShoeprint size indicates the ______size

oThe depth of a foot or shoe impression indicates a person’s ______.

oThe type of shoe can tell something of the person’s ______or ______.

oDatabases contain the names of specific ______and ______designs.

Shoe Wear Patterns

Factors that personalize a person’s footwear:

o______

oThe way a person ______

•Weight ______

•Direction of toes (______, pointing ______or ______)

oThe ______on which the person walks

oUnique ______, ______, and ______embedded in the tread.

Collection of Shoe Impression Evidence

Why would the following steps be important?

  1. Take ______as soon as possible
  2. Take ______photos of the impression from at least ______different orientations
  3. Place an ______label and a ______in position with the impression for the photo
  4. Use ______lighting when possible

Lifting Latent Impressions

Different methods to make latent prints visible:

o______makes bloody footprints visible for photography

o______the latent print reveals an impression for ______or ______

o______lifting and ______lifting techniques can capture hidden impressions

oElectrostatic ______reveals dust left with each step and creates an ______

oElectrostatic charges can lift impressions from

o_ / o
o / o
o / o

oGel lifters also recover ______impressions

Tire Treads

oTire treads—ridges and grooves channel ______away and provide ______

oPatent tread patterns—impressions made ______tire runs through a fluid material

oLatent tread patterns—impressions from tire ______used to keep tires ______and pliable

oPlastic tread patterns—three dimensional impressions left in ______surfaces

oTread patterns can indicate the ______of vehicle that left the mark

oLink a ______or ______to a crime scene

oReveal ______that took place at the scene

Anatomy of a tire:

Recording tread impressions

oCount ______and ______across the tire width

oNote unique ______—wear or ______embedded in the grooves

oCreate a ______of the suspect’s tire impressions through one ______

oCompare impressions from the ______and ______tire.

oIdentifying ______patterns may not be enough to link a suspect with a crime scene

Identifying a vehicle

oTrack widths—From ______of tire to ______of tire

oWheelbase length—From ______of front axle to center of ______axle

oTurning ______

Accident Reconstruction

oDrivers may not recall the exact ______of events before, during, and after an accident

oPeople, vehicles, and objects, however, can leave ______of their actions at the scene of an ______

oDebris patterns and tire marks can be clues to speed, direction, and vehicle identification

There are three basic types of tire marks:

oSkid marks—clues to the distance traveled after brakes are applied and the vehicle’s speed

oYaw marks—shows a sideways skid

oTire scrub—determines the area of impact

How are each of these formed?

Dental Impressions

oOccasionally a perpetrator will leave behind a bite mark—considered individual evidence

oNote differences in the size of teeth and jaws, position, fillings, crowns, caps, breakage, and crowding

Development of Teeth

Dental Patterns

oThe investigation consists of recognizing, docu-menting, collecting, and analyzing evidence

What are the two basic ways dental patterns can
be used in forensic investigations?

oThere are 76 points of comparison when comparing a suspect’s dental patterns with bite marks left at a crime scene

What is the common method used to reveal
whether there is a match?

Summary

oImpression evidence—whether patent, latent, or plastic—will be considered class evidence unless it has individualizing features.

oDebris patterns and tire marks can be clues to speed, direction, and vehicle identification.

oDifferences in dental patterns can connect a person to a crime scene.

oDocumentation (including early photos) is extremely important in an investigation.