9th Grade Forensic Science

T. Trimpe 2006 http://sciencespot.net/

What is BPA? Bloodstain Pattern Analysis

How can an investigator use bloodstain patterns to analyze a crime scene?• Location and description of individual stains and patterns•Direction a blood droplet was traveling by calculating angles of impact•Area of origin of blood source or sources•The type of object used in attack (edged, blunt, firearm, etc.)•Minimum number of blows•The positions of the victim, suspect, and objects during events•The sequence of events

http://www.crimescenetwo.com/img/popup/book2p2.jpg

Evidence from bloodstain pattern analysis is not usually powerful enough on its own to convict someone of a crime, but it can be useful in supporting other types of evidence found at a scene.

How does a blood droplet form? Click the image

for an animation.

Bloodstain Pattern Analysis Terms• Spatter – Bloodstains created from the application of force to the

area where the blood originated.

• Origin/Source – The place from where the blood spatter came from.

• Angle of Impact – The angle at which a blood droplet strikes a surface.

• Parent Drop – The droplet from which a satellite spatter originates.

• Satellite Spatters – Small drops of blood that break of from the parent spatter when the blood droplet hits a surface.

• Spines – The pointed edges of a stain that radiate out form the spatter; can help determine the direction from which the blood traveled.

• Passive Bloodstains– Patterns created from the force of gravity– Drop, series of drops, flow patterns, blood pools, etc.

• Projected Bloodstains– Patterns that occur when a force is applied to the

source of the blood– Low, medium, or high impact spatters, cast-off,

arterial spurting, expiratory blood blown out of the nose, mouth, or wound.

• Transfer or Contact Bloodstains– The pattern created when a wet, bloody object comes

in contact with a target surface; may be used to identify an object or body part.

– Wipe pattern from an object moving through a bloodstain or swipe pattern from an object leaving a bloodstain.

Images from http://www.bloodspatter.com/BPATutorial.htm

Luminol

• Used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed.

• A luminol solution is sprayed throughout the area under investigation.

• The iron present in any blood in the area causes the chemical reaction that leads to the blue luminescence revealing the location of the blood.

•Any glow detected may be documented by a long exposure photograph as the glow only lasts 30 seconds.

• Luminol only shows investigators that there might be blood in an area, since it also reacts to some metals, paints, cleaning products and plant matter. A specialist can tell the difference in the chemical’s reaction to each substance, and then perform more tests to determine whether the blood is human.

•Luminol also can point the way to other evidence or how events might have unfolded at a crime scene. If it is sprayed on a carpet and produces a glow, officers might peel back the rug to reveal a floorboard soaked with blood. It might also show the direction in which a criminal walked or dragged a body, or whether the victim was shot from behind or above.

•One problem with luminol is that the chemical reaction can destroy other evidence in the crime scene. For this reason, investigators only use luminol after exploring a lot of other options

Blood Spatter – Single Drops

• You will be creating sample drop patterns created by blood dropping from 4 different heights.

• This can be messy! Be very careful to keep the blood on the paper and not on yourself, the table, or floor. Allow the blood to dry before you move the paper.

• Obtain a piece of butcher paper (at least 1 meter long) from your teacher along with a marker, a measuring tape, safety goggles, and a bottle of blood.

• Find a space for your group in the classroom and tape your paper to the floor. Write your names on the paper and label four areas for the different heights.

25 50 75 100

Names?

• Hold the dropper bottle upside down so that the end of it is 25 cm from the paper. GENTLY squeeze the bottle so that ONE drop of blood is released and lands in the correct location on your paper strip. Repeat two more times at this height for a total of three trials.

• Continue making drops of blood on your paper, but put the drop in a different spot on the paper and change the height each time.

• Be sure the drops don’t run together!

• When you are done, leave it to dry overnight. Clean up your area and put away your materials.

25 50 75 100

Single Drop Analysis

• Now that your blood samples are dry, it’s time to do some measurements.

• Use the vernier caliper to measure the diameter of each droplet. If there are spines or protrusions on the drop, don’t include those in your measurement.

• Record your measurements in the chart on your worksheet, find the average for each height, and answer the questions.

Don’t measure the spines – just the diameter of the main area of the droplet.

Blood Spatter – Multiple Drops

• You will be creating sample drop patterns created by two droplets landing the same location from 4 different heights.

• This can be messy! Be very careful to keep the blood on the paper and not on yourself, the table, or floor. Allow the blood to dry before you move the paper.

• Obtain a piece of butcher paper (at least 2 meters long) from your teacher along with a marker, a measuring tape, safety goggles, and a bottle of blood.

• Find a space for your group in the classroom and tape your paper to the floor. Write your names on the paper and label four areas for the different heights.

25 50 75 100

Names?

• Hold the dropper bottle upside down so that the end of it is 25 cm from the paper. GENTLY squeeze the bottle so that ONE drop of blood is released and lands in the correct location on your paper strip.

• Without moving your hand, release ONE more drop onto the first drop at that height. If you make a mistake, note that on the butcher paper and try it again.

• Repeat for a total of three trials.

•Continue making drops of blood on paper – three trials for each of the four heights.

•When you are done, leave your paper to dry overnight. Clean up your area and put away your materials.

25 50 75 100

Multiple Drop Analysis

• Now that your blood samples are dry, it’s time to do some measurements.

• Use the vernier caliper to measure the diameter of each droplet. If there are spines or protrusions on the drop, don’t include those in this measurement.

• Measure the diameter of the spread – greatest distance between the satellite

Don’t measure the spines – just the diameter of the main area of the droplet.

• Record your measurements in the chart on your worksheet, find the averages, and answer the questions.

Blood Spatter - Motion

• You will be creating sample drop patterns created by dropping blood onto a paper strip as you are walking.

• This can be messy! Be very careful to keep the blood on the index cards and not on yourself, the table, or floor. Allow the blood to dry before you move the cards.

• Obtain a strip of butcher paper that is 3 meters long from your teacher along with a marker, a measuring tape, and a dropper bottle of blood.

• Tape your paper to the floor and label it with your names.

Walking DropsNames

• Hold the dropper bottle upside down so that your hand is at waist level and is over the paper.

• Starting walking along the paper strip at a NORMAL RATE and GENTLY squeeze the bottle so that blood is released ONE DROP at a time. Be sure that all the drops land on your paper strip.

Motion Drop Analysis

•When you are done with each test, draw a sketch of the blood droplets on your worksheet. Answer the questions after you have finished all three tests. Clean up your area and put away your materials.

Walking DropsNames

Walking Direction

Blood Spatter - Angle of Impact• You will be creating sample drop patterns created by droplets landing at different angles from one drop height.

• This can be messy! Be very careful to keep the blood on the paper and not on yourself, the table, or floor. Allow the blood to dry before you move the paper.

• Obtain a four pieces of paper from your teacher along with a marker, a measuring tape, safety goggles, clipboard, angle guide, and a bottle of blood.

• Set up the angle guide near the end of the table as shown below. Write your names on the four pieces of paper and indicate the angle for each test - 25o, 45o, 60o, and 85o.

Angle GuideClipboard/Paper

•Place the first piece of paper on the clip board and set it at a 25o angle from the table. Hold the bottle of blood at a height of 50 centimeters from the top of the table.

• GENTLY squeeze the bottle so that ONE drop of blood is released and lands on the paper. Repeat two more times at this angle.

• Continue testing by dropping blood from a height of 50 centimeters at each of the other angles.

• When you are done, leave your paper to dry overnight. Clean up your area and put away your materials.

http://www.fbi.gov/publications/leb/2005/feb2005/feb2005_img_29.jpg

Angle of Impact Analysis

• Now that your blood samples are dry, it’s time to do some measurements.

• Use the vernier caliper to measure the length and width of each droplet. If there are spines or protrusions on the drop, don’t include those in this measurement.

• Record your measurements in the chart on your worksheet, find the averages, and answer the questions.

Which of the three blood droplets shown would have been created by a wound in the lower part of the leg? Explain.

If you find a trail of blood with droplets that are close together, what could this mean?

If you have a blood droplet as shown at left, what does it tell you? Explain.

It has the smallest diameter so it fell closer to the ground.

Direction of spatter and fell at an angle of ~25o

The person was walking and not running. Drops from a person running would be further apart.

Vernier CalipersVernier calipers are used for small measurements, such as determining the diameter of a blood droplet.

To measure the diameter of a blood droplet, use the

caliper to measure from one side to the other. Do not

measure spines or protrusions.

1st - Read the result where the “O” on the top scale lines up with a mm mark on the center scale.

2nd - Read the result where a 1/10th mark lines up EXACTLY with a mm mark.

Caliper PracticeHow did you do?

Penny – Diameter = ________ mm

Triangle – Height = ________ mm

Rectangle – Length = ________ mm