Blood splatter & Bodily fluids

What can be learned/gained from blood stains?

*Where the crime occurred

*Manner/formation of the stains

*Point of origin, velocities, directions of droplets

*Type of weapon & number of impacts

*Sequence of events

*Consistency of witness accounts

These groups have to do with the mechanism and distribution of droplets.

Categories of Bloodstains-Passive, Transfer, Active.

Passive bloodstains

formed by the force of gravity acting alone. 

*Blood flowing directly from a wound or object containing blood.

-further subdivided into: Passive Drops, Drip patterns, Flow patterns, Pool patterns

-they tell us:

Did something/someone move around the room and drip blood?

Where did blood originate from to drip/pool/flow?

Active bloodstains

created when an exposed blood source is subjected to…

-An action or force greater than the force of gravity

-Flung from a weapon in motion

-Pressure of body expelling blood (artery or lungs/cough) 

Velocity changes due to the forces on the blood

Low Velocity

Gravitational pull up to 5 feet/sec. Relatively large stains 4mm in size and greater (circular drop shape)

Medium Velocity

velocity of 5 to 25 feet/sec. Stain size 1 – 4 mm.

*Human force behind the blood

High Velocity

Force of 100 feet/sec. and greater
Stain size 1mm in size and Smaller. Mist like appearance 

*Gunshot, coughing/expirated blood

The lower the velocity…

The bigger the stain size

Arterial wound (AKA – Arterial spurt, gush)

Blood is under the force of a person’s blood pressure due to the heart still beating.

*Wave-like pattern, Inverted V

Cast off pattern

When blood is flung from an object.

*Blood cast off of an object travels in a straight line.

*Helpful in determining the direction of movement of the weapon 

*The minimum number of impacts that occurred in the assault (one line of drops will be present for each swing/impact)

90 degree drop

circular stain with an equal length and width

Less than 90 degree stain

will be elongated or have a teardrop shape.

*Directionality is usually obvious as the pointed end of the bloodstain (tail) will always point in the direction of travel. 

Angle of impact

the acute angle formed between the direction of the blood drop and the plane of the surface it strikes

Area of origin

The common point, on a 2 dimensional surface, over which the directionality of several bloodstains can be retraced. 

Once the direction of travel & angle of impact are determined, you can find it

Transfer bloodstains

created when a wet, bloody surface comes in contact with a secondary surface that does not have blood on it.

-A recognizable image of all or a portion of the original surface may be observed in the pattern, as in the case of a bloody hand or footwear. 

Example: Footwear, handprint, hair marks, finger-prints.

Patterns can help determine the movement & possible identify of the participants of the crime scene. Shapes are sometime obvious and can be used to identify the object that created the pattern.

Evidence

-photograph!

-Clothing or fabrics with blood, Air-dried; Packaged in a paper bag

-Extremely wet items can be sealed in a plastic bag in order to transport to the lab for drying

-Refrigeration will decrease degradation of biological molecules important in the analysis of the blood.

Secretors

-80% of the population

-this means proteins/antigens that are found in the blood are also in other bodily fluids

Saliva

A mixture containing approx. 99% water with small amounts of proteins, enzymes, mucus, electrolytes, and other components.

Forensics Uses – Supports allegations of inappropriate sexual contact (biting, etc.), detection of drugs (marijuana, cocaine, PCP, heroin, amphetamines, ketamine, LSD, Rohypnol).  

*Recovered from a suspect’s body as well as eating/drinking utensils, cigarettes, stamps.

Presumptive Tests – Identify presence of amylase or squamous epithelial cells shed by the inside of our mouth.

*False positive for amylase is possible; Occurs with blood or semen.

*Cells identified microscopically

Blood type determined from saliva

Semen

*Spermatozoa cells, proteins, amino acids, hormones, carbohydrates, and a variety of other inorganic and organic compounds

*Spermatozoa cells do not have to be present in every sample.

-Drugs, alcohol, disease, and vasectomy, can drastically decrease the sperm count 

FORENSIC APPLICATIONS - Sexual assault cases (Microscopically identified)

SAP – Seminal Acid Phosphatase

*Enzyme found in high levels & present when sperm are absent

*Turns blue in the presence of semen

Confirmation Tests –

1. Microscopy – Visual presence of sperm cells

2. Identification of PSA or p30 (prostate specific antigen)

Y-Detect: Detects the DNA of male sperm cells

*Very sensitive, highly specific, all human cells are testable

Rapid Stain Identification (RSID): (basically its own agglutination test) Uses monoclonal antibodies specific for seminal fluid that don’t react with other body fluids.

*Antibodies are specific for semenogelin antigens)

Urine

eliminates soluble waste and regulates ion concentration

*Composed mostly of water & salts;  Formed in the kidneys

Forensic Applications – Search/identify qualitative presence of drugs, poisons, alcohol.

*Presumptive tests look at the concentration of urea & creatinine

Sweat

Contains hormones & proteins but can also be used to determine blood type if the person is a ‘secretor’

Bile

 Used to detect drugs, poisons in post mortem samples

Vitreous humor

Fluid behind eye lens; post mortem determination of disease, detection of drugs and poisons, and in the estimation of the post mortem interval (PMI).

How do you determine the direction of travel?

The tail of the drop points in the direction of travel.

Area of convergence/origin

The area where multiple blood drops are determined to have traveled from; The source of projected blood.

How does the appearance of the blood spatter differ from one classification to the other?

drop size & speed, as speed increases the drop size decreases