Blood in Crime Scene Investigation
Friday, October 28th, 2011At the scene of a violent crime, the examining officer is likely to find blood and traces of other bodily fluids. These are able to tell a lot about what happened, not only about how the crime was committed, but also about the people involved.
Nearly everybody knows his or her basic blood type, and whether it is A, B, AB, or 0, and Rhesus negative or positive. This division of blood into types was first done by Austrian physiologist Karl Landsteiner at the end of the 19th century. In his experiments, he took small amounts of blood and separated the red cells from the liquid, called serum. He managed this by spinning the blood at high speed in a centrifuge. Then he took the serum and added red cells from different people. They responded in two different ways: either the cells mixed with the serum, or they clumped together (clotted), which is called ‘agglutination’.
Numerous attempts at blood transfusion had been made in the past, but this observation explained for the first time why so many had failed. When introduced blood was not of the same type as that in the body, it resulted in the clumping of red cells, and the patient died. Tests of blood samples to discover whether agglutination will occur is now done prior to a transfusion being made.
DIVIDING BLOOD INTO GROUPS
Red blood cells carry substances called antigens. These help create antibodies that fight infection and disease. Landsteiner suggested that his experiment showed the presence of two specific antigens, which he labeled A and B. The discovery of these antigens allowed him to divide human blood into four basic groups:
Group A: antigen A present; antigen B absent
Group B: antigen A absent; antigen B present
Group AB: both antigens A and B present
Group 0: both antigens absent
The particular blood group of an individual depends on the genetic inheritance from both parents. Known as ABO typing, it has been used, for example, to help identify the biological father in paternity cases. How common each group is can vary from one national population to another. In the United States, for example, the relative proportions of ABO groups are roughly 39 percent A, 13 percent B, 43 percent 0, and 5 percent AB.
In 1927, Landsteiner found two other antigen types, labelling their occurrence as M, N, and MN. In 1940, working in the United States, he and A.S. Wiener discovered the Rhesus factor, named after the Rhesus monkeys they used in their investigations. Since then, other researchers have introduced more than a dozen further group systems. Different proteins and enzymes associated with specific blood groups have also been identified.
WHAT THIS MEANS FOR FORENSICS
The ability to identify blood type is a powerful tool for revealing crucial evidence in a forensic investigation. If, for example, a victim’s ABO type is O, and remains of blood of this type are found on clothing of a suspect whose type is A, there is a likely probability that they have come from the victim.
Making use of the many other blood type systems now available, this probability can be increased greatly. If blood of type 0 occurs in 43% of the population, the substance haptoglobin-2 in 36 percent of these, and the enzyme PGM-2 in 5%, then the probability of an individual having these three blood types together is 43 x 36 x 5 = 7,740 in one million. In other words, around eight people in every thousand will have this specific type of blood. It’s still insufficient to obtain a conviction on this evidence alone, but it can help to narrow the number of suspects.
In 1925, another valuable discovery was made. Around 80% of people are ‘secretors’. This means their saliva, urine, perspiration, and semen contain the same substances as their blood, and can be used for typing in a similar way. In 1940, two British researchers discovered that it was possible to distinguish between female and male body cells, in particular the white blood cells and those of the lining of the mouth. Blood typing is now so precise that recently one scientist showed that he could distinguish between the blood of his twin daughters, who were genetically identical, because one had suffered from chicken pox and the other hadn’t.
SPLASHES OF BLOOD
At the scene of a violent homicidal attack, blood may be present in considerable quantities. Not only will it be found on the victim, but also on the weapon and the surroundings. Indoors, the floors, walls, and even the ceilings may be splashed. Careful observation of these bloodstains can provide valuable clues about what took place. Bloodstains and splashes are classified into six basic types.
Round drops are found on horizontal surfaces; depending on the height from which they fell, they can spray out into a starlike shape. Splashes of blood are shaped like an exclamation mark; they show that blood has flown through the air and hit a surface at an angle. While a victim is still alive, spurts of blood result from the pumping action of the heart. A major artery can spray blood a considerable distance.
Pools of blood form around the body of the bleeding victim. If there is more than one pool, he either dragged himself, or was moved, from one area to another before dying. Smears are likely also found if this happens. Trails are left when a bloody corpse is moved. There will be drops found if the body was carried, and smears if it was dragged.
If you are looking for a Sydney Criminal Lawyer, contact Go to Court. Our Sydney Criminal Lawyer is here to help. BS14082011SCL
Sphere: Related Content
Everyone has their special memory of family barbecues when they were younger, with dad at the helm turning the meat. A spit roast can be described as the ultimate barbecue for an evening of socializing be it with friends or family. This is because the rotisserie serves as a centerpiece for the evening as well as a handy conversation starter. One of the greatest benefits of a spit roast is the ease of use compared to that of a traditional barbecue. No more slaving over a hot grill hoping that the meat is just right. The rotisserie takes care of even heat distribution as well as leaving the “cooks” hands free to actually enjoy the party.The only thing that a chef needs to concentrate on is the basting of the meat and veggies on the spit, one might favour a smokey hickory baste, or maybe a special family recipe. The options are boundless and only limited to ones imagination.