Blood in Crime Scene Investigation
, Posted in: Uncategorized, Author: farmer (October 29, 2011)
At the scene of any violent crime, the examining officer will likely see blood and traces of other bodily fluids. These can tell a great deal about what occurred, not only about how the crime was committed, but also about the people involved.
Nearly everybody knows their blood type, 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, which is called the serum. He achieved this by spinning the blood at high speed in a centrifuge. Then he took the serum and added red cells from different people. They behaved in two different ways: either the cells mixed with the serum, or they clumped together (clotted), (“agglutinated”).
A number of attempts at blood transfusion had been made in the past, but this observation explained for the first time why many had failed. When introduced blood was not of precisely the same type as that in the body, it resulted in agglutination, and the patient died. Quick tests of blood samples to discover whether agglutination will happen is now done prior to a transfusion being made.
DIVIDING BLOOD INTO GROUPS
Red blood cells carry substances called antigens. Antigens help make antibodies which fight infection and disease. Landsteiner suggested that his experiment showed the presence of two specific antigens, which he labelled A and B. The discovery of these antigens caused him to divide human blood into 4 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 a person 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 a paternity case. 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 investigated. 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 to reveal important evidence in a forensic investigation. If, for example, a victim’s ABO type is O, and remains of blood of this type are found to be on clothing of a suspect whose type is A, there is a likelihood that they have come from the victim.
Making use of the many other blood type systems now available, this probability is greatly increased. 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 8 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 reduce the group of suspects.
In 1925, another valuable discovery occurred. Around 80% of people are ‘secretors’. This means their saliva, urine, perspiration, and semen contain the same substances as their blood, and are able to be used for typing in much the same 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 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 the blood a considerable distance.
Pools of blood form around the body of the bleeding victim. If there is more than one pool, he either crawled, or was dragged, from one area to another before dying. Smears will also be found if this happens. Trails are left when a bloody body is moved. There will be drops 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
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.