Serology III Bloodstain Pattern Analysis

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Oh, the stories that blood stains tell… So far we have attempted to identify the types and looked at how DNA analysis can be done.

Now, we are going to look at physical evidence and figure out not who it came from but how it occurred….. The reconstruction of how it occurred….

Types of Bloodstain Patterns Blood drops Impact patterns Transfer patterns Smears and motion patterns

What can you learn from bloodstain patterns? Angle of deposit Distance from target Direction of travel Trails Object that caused the pattern Time since deposit Volume of blood

Factors affecting bloodstain patterns Energy Low Medium High Distance Target surface Angle of deposit

Low velocity patterns Low velocity spatters happen when an object moving less than 5 ft/sec strikes a surface, with drops that are 4mm or larger in size. Example: Blood dripping only under the influence of gravity…. The drop will change shape depending on whether or not the source is standing still or moving

Low-velocity pattern

Low velocity patterns cont. Arterial bleeding – If an artery is damaged during an assault, suicide attempt or accident, the blood loss may take the form of gushes or spurts.

Low velocity patterns cont. Cast-off blood – blood that is flung from an object

Cast-off blood tends to be a fairly uniform trail of droplets. You can figure out the point of convergence as well as the number of blows with the weapon that made contact to the victim. You can figure out the position of the assailant, the height of the perpetrator and even if the assailant was right or left handed.

Ahhh…now the Medium velocity spatters Medium–velocity spatters come from objects moving between ft/sec. The spatters are generally smaller than the big ol’ low velocity ones. They vary from one to four millimeters in diameter. Example – Spatters caused by blunt objects

Medium-velocity

High-velocity spatters High-velocity spatters occur when an object strikes a victim at a speed faster than 100 ft/sec. The spatters are very small, mist-like patterns and are generally less than 1 millimeter in diameter. Example: A bullet produces spatters near an entrance wound or an exit wound.

High-velocity spatter FYI: The spatter that a bullet causes is different depending on whether the bullet is entering or exiting the victim.

Which way did it go? A drop of blood ‘on the move’ will leave a tail. The tail points to the direction that the blood was traveling. This would then reveal the direction of the origin.

Where did the blood come from? Click on hammer!

Angle of Impact Now that we know how to figure out the direction of travel, we can determine the angle of impact. Take out your calculators. Sine of impact angle = width of bloodstain (mm) length of bloodstain (mm)

Math time…. Suppose that a drop of blood measures 10 mm in width and 18 mm in length. At what angle did the drop hit the target?

Area of Convergence The area of convergence represents the point from which a stain emanated.

Area of Convergence

Void Patterns A void pattern is an absence of blood spatter in an area where you’d otherwise expect to see them. Many times something blocks the spatter and creates what looks like a white shadow among spatter patterns. Many times this void indicates where the attacker stood.

Transfer Patterns Contact – transfer Motion: Wipe vs Swipe So, there is a difference?

Transfer patterns result when an object soaked with blood comes in contact with an unstained object. Example: Bloody fingerprints and shoeprints

What caused the transfer of these patterns?

Are you telling me that there is a difference between a wipe and a swipe ?

To wipe or to swipe, that is the question…….. Wipe - pattern created when a secondary target moves through an existing wet blood stain on some other object Swipe - the transfer of blood onto a target (clean) surface by a bloody object that is usually moving laterally

After all, you don’t call them windshield swipers, right?

Facts about Blood –Accounts for 8 % of total body weight 5 to 6 liters of blood for males 4 to 5 liters of blood for females –A 40 percent blood volume loss = irreversible shock (death) –A blood loss of 1.5 liters = incapacitation

Homework Questions 1.Describe the different types of blood stain patterns. 2.What can you learn from bloodstain patterns? 3.Give examples for low, medium and high velocity patterns. 4.What is a void pattern? 5.What is the difference between a wipe and a swipe?