What can ancient bones tell us? how can ethnicity be told from bones?.
Bloodstain pattern analysis (BPA) is the interpretation of bloodstains at a crime scene in order to recreate the actions that caused the bloodshed. Analysts examine the size, shape, distribution and location of the bloodstains to form opinions about what did or did not happen.
To help reconstruct events that caused bloodshed, analysts use the direction and angle of the spatter to establish the areas of convergence (the starting point of the bloodshed) and origin (the estimation of where the victim and suspect were in relation to each other when bloodshed occurred).
The general role of the Bloodstain Pattern Analyst in a criminal investigation is to assist in the reconstruction of those events of an alleged incident that could have created the stains and stain patterns present at a crime scene, on items of physical evidence recovered from that scene and on items of clothing that …
Area of Origin -‐ The three-‐dimensional location from which blood spatter originated. Backspatter Pattern -‐ A bloodstain pattern resulting from blood drops that traveled in the opposite direction of the external force applied; associated with an entrance wound created by a projectile.
Properly collected and preserved blood evidence can establish a strong link between an individual and a criminal act. Blood evidence or the lack of blood evidence can also be used to bolster or contradict a witness statement or any statements that the suspect may make.
Bloodstain pattern analysis provides important forensic information about the crime under investigation; it tells what happened. … Every effort must be made to preserve the crime scene until the bloodstain evidence has been investigated.
Once doctors differentiated blood into distinct types, they could use that information to safely perform blood transfusions. Furthermore, forensic scientists can use that information to exculpate people suspected of some types of crimes, and they can use it to help determine the paternity of children.
Patterns of drying help analysts determine how long an assault went on, detect whether it took place all at once or in stages, and nail down possible crime scene contamination [source: Wonder].
The First study of blood spatter analysis came from Dr. Eduard Piotrowski, in 1895 he wrote “Concerning the Origin, Shape, Direction and Distribution of the Bloodstains Following Head Wounds Caused by Blows”. With this writing piece it influenced many investigators in the early 20th century.
Using elastic string, the analyst draws lines from each spatter through the level line. Then, he or she uses a protractor on the level line in the area where the strings converge to determine the angle of flight for each spatter.
Based on the varying sizes and shapes of the blood drops, investigators can often tell what type of weapon caused the spatter, determine the general area where the attack occurred, and track the positions of the victim. … “Oftentimes blood spatter analysis is used to test an alibi, such as self-defense,” Johnson says.
This understanding is important, because the interpretation of blood spatter patterns and other evidence at crime scenes may reveal important investigative information, such as the positions of the victim, assailant, and objects at the scene; the type of weapon that was used to cause the spatter; the number of blows, …
The test to determine your blood group is called ABO typing. Your blood sample is mixed with antibodies against type A and B blood. Then, the sample is checked to see whether or not the blood cells stick together. If blood cells stick together, it means the blood reacted with one of the antibodies.
In addition to microscopic evidence, the trace evidence section also deals with physical evidence such as tire and shoeprint impressions. These can be found in several different types of materials, such as paint, blood, soil and dust.
A Centrifuge spins the blood samples at 3000 RPM for five minutes, forcing the cells to the bottom of the sample and leaving the serum at the top. This allows the contents of the serum to be analysed without interference from the cells.
An investigator may discern the direction of travel of blood that struck an object by studying the stain’s shape. As a stain becomes more elliptical, its direction becomes more discernible because the pointed end of a bloodstain faces its direction of travel.
Bloodstain pattern analysts sometimes are called to gruesome scenes to gather crucial evidence regarding violent crimes. … Analysts can determine the trajectory of a projectile, the number of wounds a victim suffered, and how events unfolded during a violent crime.
Phenolphthalein is a presumptive test that reacts with the heme molecule present in blood. A positive reaction gives a pink color. While bloodstains normally appear red-brown in color, the color of the substrate or the age of a stain may affect the appearance or visibility of the stain.
- Identify Scene Dimensions. Locate the focal point of the scene. …
- Establish Security. Tape around the perimeter. …
- Create a Plan & Communicate. Determine the type of crime that occurred. …
- Conduct Primary Survey. …
- Document and Process Scene. …
- Conduct Secondary Survey. …
- Record and Preserve Evidence.
Blood type tests are used to check what blood type you have. Your blood is “typed” according to whether certain markers, called antigens, are present on the surface of red blood cells. The two most common blood type tests are the ABO and Rh tests.
Rhesus (Rh) factor is an inherited protein found on the surface of red blood cells. If your blood has the protein, you‘re Rh positive. If your blood lacks the protein, you’re Rh negative. Rh positive is the most common blood type.
Luminol, leuchomalachite green, phenolphthalein, Hemastix, Hemident, and Bluestar are all used as presumptive tests for blood.