Ch.2 Crime Scene Bloodstain Pattern Analysis

What is crime scene bloodstain pattern analysis?

The application of scientific knowledge to examine and interpret the shape, sequence, and distribution of bloodstains related to a crime.

What can bloodstain pattern analysis help determine?

• Sequence of events

• Approximate location of the blood source

• Positioning of the victim

• Position, intensity, and number of impacts on the blood source

• Manner of death

What is the average blood volume in an adult?

Approximately 8% of body weight.

What are the main components of blood and their characteristics?

Cellular portion: blood cells and platelets

Plasma: mostly water, with proteins, inorganic salts, and other organic substances

Mass and density slightly greater than water

How does blood clotting work and why is it important?

Blood forms clots (thrombi) through coagulation to stop bleeding

• Coagulation begins after injury

• Coagulation time for 1 mL venous blood in glass tube is 5-15 minutes

How does viscosity affect blood droplet formation?

Controls flow — thicker blood moves slower and forms rounder drops; blood viscosity is 5 times greater than water.

What role does surface tension play in blood droplets?

Maintains droplet shape and influences splatter and satellite stains; causes drops to hang and form pendant shapes.

How does cohesion force affect blood droplets?

Keeps blood molecules together, maintaining drop integrity and resisting breakup.

What impact does gravity have on blood droplet stains?

Drives movement and impact energy, affecting stain size and spread.

How does the texture of a surface influence blood stain patterns?

Smooth surfaces cause less distortion around edges than rough or porous surfaces.

What is the purpose of chemical reagents in blood detection?

They react with blood to produce color, chemiluminescent, or fluorescent light; very sensitive and used to enhance detection, especially for latent bloodstains.

What is luminol used for in bloodstain analysis?

Locating bloodstains at a crime scene.

How should bloodstain patterns be documented at a scene?

• Photography: overall, mid-range, and close-up shots

• Use lens parallel to surface to avoid distortion

• Note-taking and sketching

How does external force affect bloodstain size?

Increasing force reduces surface tension, producing smaller, higher-velocity droplets.

What characterizes low velocity impact spatter?

Velocity less than 1.5 m/s; stains larger than 4 mm in diameter.

What characterizes medium velocity impact spatter?

Velocity between 1.5 to 7.5 m/s (typical for beatings or stabbings); stains 1–4 mm in diameter.

What characterizes high velocity impact spatter?

Velocity greater than 30 m/s (firearm-related); stains less than 1 mm in diameter.

What is directionality in bloodstain pattern analysis?

Characteristics of a bloodstain that indicate the direction the blood was moving.

What does the shape of the parent stain indicate?

It's an elongated ellipse that shows direction of travel.

What are satellite stains and spines, and what do they show?

Satellite stain: a smaller stain formed during creation of the parent stain

Spine: points away from the parent stain and toward the direction of travel

What is the angle of impact in bloodstain pattern analysis?

The acute angle (α) at which a blood drop strikes a surface, relative to the surface plane.

How does the angle of impact affect the shape of a bloodstain?

• 90° angle = circular stain

• Less than 90° = elongated stain

• The smaller the angle, the more elongated the stain becomes

What is the area of origin in bloodstain pattern analysis?

The location from which the blood spatter originated; determined by analyzing multiple elongated spatter stains.

What is the string method for determining area of origin?

• Calculate the angle of impact for multiple well-formed, elongated stains

• Attach one end of a string to each stain

• Use a protractor to set the string path according to the angle of impact

• Strings converge at the area of origin