Crime Scene Exam 3

An expert witness is a person who:

Is skilled in a specific occupation or trade and, because of this skill/knowledge, is qualified to analyze or compare a stated set of facts and render an opinion based upon those facts.

Qualifications of an expert witness.

Education, training, licensing, board certification, specific experience in their area of expertise.

To establish credibility of an expert witness, the counsel needs to establish:

• the actual practical work experience related to the subject in which the expert is testifying, including when, how long, how recently the experience has been gained

• whether the expert has formal education or is “Self-taught”

• prior court experience

• extent of specialized training acquired

Perforation

Bullet passes through and exits.

Penetration

Bullet enters but does not exit.

contact wound

muzzle of weapon is in contact with the tissue or the clothing covering the tissue

Near contact

no more than 5 in from wound

Intermediate range

Between 5 and 40 inches from the wound.

Characteristics of a contact wound

• Edges of the wound are seared by hot gases from the gun

• there is soot embedded in surrounding skin/fabric.

• There generally will not be gun powder particles visible because they enter the wound.

Distance wound

Lack of soot, searing, or powder

Three types of trajectory analysis

Internal ballistics

External ballistics

Terminal ballistics

Ricochet

A projectile making glancing contact with a surface and continuing flight.

 Internal ballistics (Conducted by a forensic firearms examiner)

The processes involved inside the gun as the bullet is fired and travels down the barrel

External ballistics (Conducted by the crime scene analyst)

The events that occur after the bullet leaves the barrel of the gun but before it strikes its target

Terminal ballistics (Conducted by a forensic pathologist)

Defining the path of a bullet through the body, the associated damage and differentiating entry from exit wounds

Deflection

when a bullet changes direction due to factors like wind, impact with an object, or for moving targets

Rifling characteristics

Lands and grooves on the surface of a projectile created by traveling through the gun barrel.

Range determination

Using the weapon and similar ammunition to create gun powder residue standards at different distances

Items in a trajectory kit

Trajectory rods, centering guides, angle finders, lasers (sometimes)

Trajectory

A fired bullet's path.

Most accurate way to determine bullet trajectory over a short distance.

Connect two impact locations separated by sufficient distance via laser or trajectory rod.

How to recover fired components

Cut into walls (being careful of electrical wire and pipes)

Cut off a piece of fabric (Cut three sides of a square a sufficient distance away from the hole and then fold the fabric back.)

Cut into a solid structure (Cutirregular shapes and mark a direction.)

footwear

• leave impressions

• wear and tear can lead to differences in impressions

• crime lab can observe these marks

Inclusion

known shoe did make impression

Could have made impression

known shoe could have impression

exclusion

known shoe did not make impression

inconclusive

insufficient clarity in either questioned or known impression

3 types of impressions

3D, visual (2D), hidden (2D)

Scaled photos

• 90 degrees to impression

• 1 impression per frame

• fill entire viewfinder with scale