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Class Characteristics

a. Describe the physical object and limit (but not eliminate) the likelihood that similar objects exist.

b. The greater the number of class characteristics that can be associated with a given object, the smaller the category within which the object can be placed.

c. The larger the number of class characteristics, the greater the value in an investigation.

d. Physical evidence with class characteristics may have more than one possible source.

Individual/Identification Characteristics of Physical Evidence

a. Establish a physical object's difference/uniqueness from all others within its group.

b. Establish the unique identity of an object or its source to the exclusion of all others.

c. Examples:

(1) Fingerprint impressions

(click on photos for larger view)

csr-afisprint1.jpg (34740 bytes)  

csr-afisprintout.jpg (63247 bytes) 

(2) DNA analysis

(3) Ballistic examinations

csr-gunshotwound.jpg (40112 bytes)  

csr-crimescene3.jpg (31666 bytes)  

(4) Footwear/tire impressions
csr-footwearimpr.jpg (33234 bytes) 

Mathematical Probability

  1. The probability of any given occurrence at a specific place or time relates to the value of a piece of physical evidence. 

    Example: The likelihood of two different people sharing an exact print (type, characteristics, spatial and planer relationship) is 1:10.

  2. The less frequent the rate or probability of independent occurrences, the firmer the base of confidence becomes.

  3. The greater the frequency of an occurrence, the less significance that can be attached to its evidentiary value.

Examples:

  • 1969 yellow VW Beetle is observed in commission of a hit and run in  1969.

In 1969, yellow VW Beetles were common (popular car, limited color selection).
The chances were greater that two yellow 1969 VW Beetles could exist in the same vicinity in 1969 than today.
Therefore, this information may lack significance in 1969.

  • 1969 yellow VW Beetle is observed in commission of a hit and run in 2001.

1969 yellow VW's (and VW's in general) are less common in 2001.
Therefore, the rate of occurrence of the presence of a yellow VW Beetle would be significantly less.
Thus, the odds (mathematical probability) would favor such a vehicle being the suspect vehicle if found in the vicinity/jurisdiction where the hit and run occurred.
The presence of fresh damage would also impact the odds.

Theory of Transfer/Exchange

a. "When two objects touch each other, trace substances of each are exchanged."

b. When a suspect enters a crime scene, he/she leaves something behind and/or takes something away from the scene.

c. This provides an opportunity to link suspect with the scene/crime providing proper collections/examinations are made from/of scene/victim/suspect.

Major Groupings Of Physical Evidence

a. Physical evidence is any material, however microscopic, solid, liquid or gaseous, that may aid in the determination of the truth during the investigation of a crime.

b. Physical evidence capable of scientific analysis that is likely to be found at the scene of a crime falls into eight (8) major groups and one (1) miscellaneous group.

(1) Weapons - I.D.

csr-weapongun.jpg (20871 bytes) 

 csr-knife.jpg (17165 bytes)  

csr-knifewounds.jpg (29843 bytes) Knife wounds

(2) Blood, saliva, and semen - I.D.

(3) Latent impressions - I.D.

(4) Shoe and tire impressions - I.D.

(5) Tool Marks - I.D.

(6) Questioned documents - Class to I.D.

csr-ninhydrin.jpg (39252 bytes)  
Fingerprints: using ninhydrin 

(7) Soil - Class

(8) Glass - Class

csr-brokenglass2.jpg (39134 bytes)
Broken glass - attempted point of entry

(9) Miscellaneous trace evidence such as hair, fibers, paint chips, and  bomb residue - Class

Physical Evidence - Point of Entry

a. Subject tends to be nervous and in a hurry at this point and is often somewhat careless.

b. Physical evidence to look for at the point of entry.

(Examples shown are possible evidence that may be found and collected at the crime scene, but are NOT all inclusive.  The only evidence that cannot be found is that which is not looked for.)

csr-gloves.jpg (18960 bytes)
Trace fibers/prints from subject’s clothing/gloves

csr-brokenglass3.jpg (17571 bytes)
Blood
(breaking glass often causes cuts.)

  • Tool marks

  • Hairs

  • Splintered wood

  • Chipped paint

csr-brokenglass.jpg (55426 bytes)
Broken glass (inside/outside)

csr-handonblind.jpg (28522 bytes)
Latent prints (finger/palm)

csr-ftprintac.jpg (24199 bytes)
Footprints (inside and outside)

csr-brickprints.jpg (32462 bytes)
Discarded items/tools

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