Analysis of Biological Evidence

All bodily fluids should be visually assessed before any samples are taken and sent off to the lab, this includes photographing the fluid and looking for different contrasts. There have been a large number of incidents where samples have been taken, sent off to the labs to test and the bodily fluid has been mistaken for something that would be used for cooking, this not only wastes time and makes the investigation go on for longer but it also wastes a large amount of money. There are three main presumptive tests that forensic scientists can do at a crime scene to see if the substance is blood or not. They are Luminol, Kastle Meyer reagent and Leucho Malachite Green (LMG).  Blood tests are based on colour change, or the chemiluminescence of a reagent when it comes in contact with haemoglobin.

Luminol is a chemical that is a very useful tool for forensic scientists as it can show blood that has been cleaned up, even after a criminal has attempted to clean up blood it cannot be completely removed from a surface, there will be a small trace left behind. After the scientist has added the luminol solution to a location where blood has been a reaction called chemiluminescence takes place (which is releasing energy in the form of light), this happens due to a chemical reaction taking place, which leaves a blue coloured glow on the traces of blood left behind.

Kastle Meyer is a simple quick test for blood and is the test that I did in class. It involves transferring the substance onto a swab or pad and then adding hydrogen peroxide, the Kastle Meyer reagent and ethanol to a sample, if it is blood then haemoglobin is detected which causes a reaction to occur which will turn the substance pink, if it is not blood then no reaction will occur resulting in no colour change.

Leucho Malachite Green (LMG) – Is a very similar test to kastle meyer but it needs different materials to work. It is now no longer used because of the amount of false positives it gave and its high level of toxicity. It was known to react with metals as well which was a big problem when the substance that you wanted to test was on a piece of metal. To do the LMG test you must get some of the blood sample using a deionized swab, once some of the blood is on the swab around one or two drops (depending on the amount of the blood sample) of the LMG solution can be added, if the swab changes colour (usually to a blue/green) then the test is inconclusive and can’t be used. If the swab keeps its original colour, then the next step can be done. Then one to two drops of hydrogen peroxide (3%) should be added, if the colour now changes to a blue/green then the results is positive and blood is present.

The race of a person can usually be told upon a visual inspection of the hair shaft. For example, if the hair is thick and round then it will be Asian hair, if the hair has a squashed appearance then it will be African hair and if it is oddly shaped or a combination of different shaped hairs then it will be European hair. A visual inspection can tell the scientist where on the body that hair has come from. For example, if the hair is tapered (starts thick and goes thin towards the end) then the scientist can assume that the hair is an eyelash. Another example would be if the hair has a kinky or curly shape, if this is the case then the scientist that is examining the hair can assume that it is a pubic hair. The two main stages that a forensic scientist would need to go through when examining a hair is a visual analysis and a microscopic analysis.

OJ Simpson

In the case where OJ Simpson allegedly murdered Nicole Brown Simpson and Ronald Goldman a lot of evidence was found at the scene of the crime, most of the evidence found could be linked to OJ Simpson in some way. One of the most useful pieces of evidence found at the crime scene were a set of bloody fingerprints that where believed to belong to OJ Simpson, as well as a trail of footprints that led right from the bodies out of the house, these where also believed to be OJ's footprints. It was later found due to extensive research that the blood the fingerprints were made out of was in fact OJ's as well as the fingerprint itself being a strong match according to reports. At the time OJ also had cuts on his hand which he claimed was from cooking, the problem being the cut on his hand was not of a large enough size to produce the amount of blood that the fingerprint was found in at the scene,

Hair fibers were also found at the scene but none had any root balls attached which meant that the DNA of the hair could not be tested against OJ. Instead the forensic scientists had to perform visual and microscopic tests to see if the hairs belonged to OJ, from the examinations that they did it was concluded that the hair fibers found at the scene was not a match to OJ Simpson