Collecting Evidence

There are three categories of evidence which can be collected from a crime scene, Physical, Chemical or Biological.

Physical Evidence

Physical Evidence are items which are present at the scene and do not involve a chemical or a bodily fluid; for example a footwear mark or fingerprints. It is important to collect physical evidence so that it can be taken back to a laboratory and tested for important information. The most common form of physical evidence are fingerprint , which are left at most crime scenes. Fingerprints are one of the best forms of identifying who was at a crime scene, due to every single persons fingerprints being completely unique to the individual. Fingerprints are developed during pregnancy, meaning that even babies have unique fingerprints, and not even identical twins have the same Fingerprints.

Fingerprints are left when the different materials found on the finger come into contact with a surface, and leave a print in the shape of the fingerprint pattern. The materials found on the finger are usually excreted from the glands present on the finger. There are three glands, including the Eccrine Glands, which produce Chlorine, Urea and Amino Acids, The Apocrine Glands, which produce Irons, Proteins and Carbohydrates and finally the Sebaceous Glands, which produce Fatty Acids, Alcohol and Hydrocarbons, however, most Fingerprints are actually 99% water. Fingerprints are also often left when the finger has previously been contaminated by another substance which is then transferred onto an item touched by the finger, such as a drink can or computer monitor.

When it comes to lifting a fingerprint, there are numerous factors that need to be taken into account, such as the surface the print is being lifted off, like is it smooth or rough, how long the finger was in contact with the surface to leave the print, the longer the better, and the weather when the fingerprint was left. All of these factors contribute to the method you would use to lift the fingerprint, as there are numerous methods depending on the environment, in which the print has been left.

One method of Fingerprint Enhancement that would be using simple black or white powders, to dust the fingerprints lightly, in order not to smudge the print, as this could lead to the evidence being useless. The powder sticks to the grease and water left by the fingerprint and leaves a clear outline, which is easily pictured, and lifted using J-Lar tape and clear plastic. When lifting a fingerprint, it is crucial not to smudge the print, or leave air bubbles as these can corrupt the results, as they cannot be seen by the computer analysing the print. These are usually used because, as previously stated, they are easily photographed, and stand out well on matt backgrounds. However, on surfaces with multiple colours, it is best to use a Fluorescent powder, as these are also easily photographed, as stands out on multi-coloured backgrounds, whereas black powders may not show clearly, which could lead to the evidence being inconclusive. It is good for the fingerprints to be as clear as possible as to show a jury the proof behind your conclusions. 

Fingerprints Lifted from the scene are packaged up safely, often within an envelope, once the fingerprint has been lifted and stuck to a piece of plastic. The evidence container will then be signed by the person who collected the evidence with an evidence number, so that the evidence can be easily cataloged for future reference.

However; the most important thing to take into account when lifting fingerprints is to make sure that the person collecting the evidence has their full PPE on, and is not leaving their own fingerprints at the scene, as this would contaminate the evidence ,and bring the accountability of the evidence into disrepute. 

OJ Simpson Case

During the OJ Simpson Investigation, there were fingerprints lifted from the scene, however there was a phone just inside the pen door of the crime scene which could have been used by the attacker, and therefore clearly should have been dusted for prints; however Robert Risk the First Attending Officer to the scene thought it best to pick up the phone without using gloved in order to call the police station for backup. In doing so, he contaminated any fingerprints evidence which may have been present on the telephone. 

Mark Furman also documented the presence of a bloody fingerprint on the gate as you entered the crime scene in his brief initial scene assessment, however upon passing this information on, no action was taken, meaning that the print was likely lost to the elements. Had this print been collected it could have likely belonged to the assailant which could have resulted in a vastly different verdict for OJ Simpson. 

Also found at the OJ Simpson Case were footwear marks, however these were likely the result of officers and the SOCO team not wearing the appropriate footwear protectors. 

One of the most crucial forms of Physical Evidence withing the OJ Simpson case was the glove which was found at the back of OJ Simpsons pool house, and the counterpart which was found at the crime scene. The gloves were a match and were collected correctly, being placed into a brown paper bag- however the investigation fell through when OJ showed in court that the gloved didn't fit. 

Biological Evidence

Biological Evidence is any evidence which has been obtained from the body, such as skin fragments, blood or semen.It is important to collect Biological Evidence form the scene so that it can be taken back to a laboratory and tested for important information. One of the most common forms of biological evidence, depending on the scene, is blood. Which is often left a scene whenever there is a violent nature to the crime. 

Blood can be identified at a scene by performing a presumptive test on the substance you believe to be blood. The test will give you either a positive or negative result, therefore telling you whether the substance is in fact blood or not; however for further information the a sample would need to be taken back to the laboratory for further testing. 

The most common presumptive test used to identify the presence of blood is the Kastle Meyer Test First, the SOCO would add Hydrogen Peroxide to the suspected blood sample, and then the Kastle Meyer Reagent. Finally, ethanol would be added, upon which an enzyme called Peroxidose reacts with the chemicals added to produce a pink colour, if blood is present. This would be the most reliable presumptive test at a crime scene as there is less likelihood of false positives; however one can produce if there is any presence of an oxidising agent in the sample, such as rust. This however is not as common a false positive as Luminol, another presumptive test for blood and is therefore the most common presumptive test performed by forensic scientists, Luminol being a chemical which in the presence of blood, emits a blue/green light. The Luminol however is known to react with a number of different chemical as well as blood therefore making Kastle Meyer the dominant presumptive test. 

Once the presence of blood has been ascertained the blood needs to be collected for testing back at the laboratory. If the blood is on the floor, the blood can be taken out of context by swabbing the blood using a specific cotton tip evidence container which will swab the blood from the floor and into the container. This can then be labelled correctly and placed into the chain of custody. 

If the blood is being collected in context, for example if a piece of clothing is soaked in blood, and the entire piece of clothing is being collected in order to get a larger sample - the evidence must be placed in a paper bag in order to allow the blood to "breathe" so that the blood doesn't denature. 

OJ Simpson Case

The crime scene of the OJ Simpson case had a substantial amount of blood, from both Nicole Brown Simpson and Ron Goldman; though this is to be expected. The blood evidence in the OJ Simpson case which is helpful to the case was the blood found on the door and inside OJ Simpsons Ford Bronco, as there were smearing's of blood on the vehicle the night of the murder. Gary Sims, the lead Forensic Investigator on the OJ Simpson Case testified in court that the blood inside the bronco was consistent with blood taken from OJ Simpson, Nicole Brown Simpson and Ron Goldman, however this evidence was not enough for a conviction, as the defense argued that the blood had been planted - as there was evidence of some of OJ Simpsons blood going missing, at which point the Defense team argued that Simpsons blood had been planted alongside Nicole Brown Simpson and Ron Goldman's.

There was also DNA of Simpsons found on Nicole's body, which if collected correctly would have been damning evidence- however the body was draped in a blanket found inside the house in order to cover the body from the press. In draping the blanket over the body, any and all evidence on the body was corrupted as Simpson would have had access to the blanket, therefore explaining why his DNA would be on the blanket and therefore the victim.

Chemical Evidence 

Chemical Evidence can usually be described as anything which has been artificially made such as drugs or gunpowder.   When analysing Chemical Evidence there are a multitude of factors that you need to take into account, such as where the evidence can be found, how to test for it, and how it can be used, just like all other forms of evidence analysis. A chemical reaction occurs when two chemicals react to form another. This reaction can usually be detailed, and be used as evidence given the right conditions.

Drugs are very commonly found at crime scenes, as they are illegal, they are a common source of crime, as crimes are often committed in order to obtain, and as a results of drugs.  Illegal drugs are divided into 3 classes, Class A, B, and C. A being the drug with the most illegality behind it and C being the least, however all are illegal. 

First when identifying drugs, it is important to perform a visual inspection; for example if there is a large pile of white powder next to some scales in a room which isn’t a kitchen, it is likely that the sample will be drugs. Also, when investigating drugs, it is important to determine between whether the drugs are for personal use, or if they are intended for distribution. As using Heroin for example will simply result in the drugs to be taken from you and a warning, whereas is you have an amount of heroin which could not feasibly be used by one person, that is classes as intent to deal, which results in a large prison sentence.

As drugs are not always easily identifiable at sight, there are spot tests to be done at the crime scene in order to determine if the substance is an illegal drug, and if so which illegal drug is it. 

Any drugs which are within the categorize of "Hydrocarbons" meaning that they are made up mostly of hydrogen and carbon in different quantities-  can be identified through the Marquis Reagent which will change a different colour based on the type of drug, for example Heroin turns Red, and Ecstasy will turn blue. 

OJ Simpson 

There was very little chemical evidence obtained from the OJ Simpson case, as there was no gunshot, therefore meaning that there was no gunshot residue to test for, and there were no drugs found at the scene, therefore meaning that there was nothing there to collect or test for.