Blood Spatter #3 - Marvelous Ms. M's Science Page

Blood Spatter Patterns Bits and pieces Use of force to describe the blood spatter In the past, forensic investigators used velocity to describe a pattern of blood dispersion. Low velocity (gravity/drop, 5ft/s) medium velocity (punch, 25ft/s)

high velocity (gunshot, 100ft/s) While velocity described the speed and direction of the blood spatter dispersion Force describes impact. To find the force, F=ma, which is measured in Newtons F=force m=mass a=acceleration The goal is to describe the stain first, then determine the impact force

Other Blood Spatter Patterns Blood flow patterns High elevation to low elevation Shows if a body has been moved Arterial Bleeding Typically found on walls or ceilings and are caused by the pumping action of the heart Blood Trails Show directionality

One end of the blood drop will be more scalloped than the other Shows movement of the victim Blood Pools Pools of blood form around a victim who is bleeding heavily and remains in one place If victim is moved,

May appear to be droplets or swipes/wipes connecting first location to second Cast off Patterns Show where a person was standing (suspect/assailant) Does not indicate what weapon is used Transfer Pattern Any pattern that occurs when a bloody object or

surface comes in contact with another object or surface. Transfer Pattern Sometimes the transfer pattern can assist in identifying the bloody object.

Swipe A swipe occurs when a bloody object moves across a clean surface and deposits blood on that surface. Wipe A wipe occurs when an object moves through and disturbs wet blood that has

already been deposited on a surface. Dark ring around blood drop = skeletonization Starts drying at perimeter Wiping through blood at different times gives different skeletonization Sequence of Events Blood Spatter Analysis

Lines of convergencetwo or blood spatters can pinpoint the location of the blood source (forms area of convergence) 13 Blood Spatter Analysis Six Patterns Describe each of these: a) Passive drops

b) Arterial gushes c) Splashes d) Smears e) Trails f) Pools 14 Scenario next class! Discuss roles for next class Lead investigator

Make sure all steps are covered in correct order Keep squad on task Assist any squad member with their task Take lead on assigning roles to complete the investigative report Photographer 3 images for each scene

Detailed photos for 5-6 blood spatters for analysis later (if needed) Responsible for uploading photos into report Crime scene Sketcher Record scene measurements Sketch (general) location of blood spatter Record 5-6 width/length measurements for analysis

Evidence technician Presumptive blood test Measure blood spatters (5-6) for width and length-make sure photographer takes pictures of these Evidence Technician 2 Assist with angle of impact calculations Set up strings to determine area of

convergence Steps on Scene 1. 2. 3. 4. 5. 6. 7.

Photograph scene Presumptive blood test Sketch and measure scene Determine how many impacts are on scene Pick 5-6 spatters/direction of impact to calculate angle of impact Use stringing method to find area of convergence Photograph after strings are set up and document height, distance of blood travel from convergence Stringing Method 1. Find angle of impact:

1. width/length of blood spatter 1. Actual size doesnt matter, you can measure on a photo as the ratio will be the same 2. Sin-1(width/length) 2. 3. 4. 5.

Put a protractor along the long axis of the spatter Tape string to the bottom of the stain Move the string until it matches the angle of impact and tape down Repeat for 5-6/direction of impact

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