The scene preservation should be maintained by anyone entering the crime scene, as it will help to prevent the loss of evidence by contamination such as finger prints, the taking away of evidence for example fibres sticking to the bottom of a shoe, and the moving of evidence, this can be as simple as closing a window.
The crime scene is considered to be an area or location that may contain evidence, which maybe in link to a crime which has been committed or most likely be committed at a later date. When going into a crime scene a systematic needs be used and any findings recorded, in a clear and accurate way. It is often best to do it at the time of investigating, this can not always be possible such as in scenes were the examiner has to deal with people in distress. Were the report can not be done at the time it should be done as soon as possible afterwards, to ensure that no information is lost are forgotten. The notes should include plans and measurements, so it can later be described in court.
There are many methods of recovery of evidence such as handpicking, removal of the whole item, brushing which is used for finger prints and footprints, tape lifting which is often used for the collection of fibres are hair that has fallen out. Swabbing and scraping can be used in the collection of blood samples, or collection of dry or wet liquid at the crime scene. Casting is also used for collecting evidence such as footprints and casts of weapon marks.
Once the evidence has been collected it must be packed in the correct packaging to prevent damage, loss and contamination of the evidence. The packaging should also be labelled containing information on the description of the item, and exhibit number, reference number, were it was recovered, the time and date and the signature of the Crime Scene Investigator.
DNA is one of the most powerful methods of been able to identify a person, who might have been involved in a crime. It is found in nearly all the cells in the body, and contains all the genetic information of that person, with in the nucleus of the cell. As each child inherits a different combination of DNA from the parents then they have a unique combination. The only exception is identical twins that will have the some DNA. DNA can also be collected from the mitochondria, the is mitochondrial DNA, it is only inherited from the mother. It is used for identifying decomposed bodies, hair, bones and faeces. DNA can be found in the blood, semen were at lest 600 cells are need, but this is a small amount is considering that in the average ejaculation 350,000,000 sperms cells are released. Saliva can be used; there is no DNA in the saliva but in the buccal cells in the side of the mouth. Hair palled out at the root will provide DNA, but shed hair will only contain mitochondrial DNA, and one of the other forms of DNA is vaginal fluid which contains cells from the lining of the Vagina. Any DNA collected will go on to the National DNA database, were it is checked against other crimes on the data base
At any crime scene health and safety needs to be maintained, and were the scene is not at an acceptable level of safety then it should not be examined, until its safe. One of the main hazards at a crime scene are biological, this often posses little risk if the correct investigation process is followed. This is in five basic steps. The first step is to identify any hazards present, step two is to consider who and how the person may be harmed, the third step is to evaluate the risks and make a decision on how to act this can include existing precautions and what are the adequate clothing which needs to be worn, step four is the recovery of finding and step five is reviewing of the assessment and revising it.
The main health and safety risks at a crime scene are inhalation of toxic products into the respiratory system. Skin contact, were contaminations is cased by contact are absorptions of the substance. Ingestion, injection, viral disease which can be from blood stains wet or dry. The health risks can also be from fuels and lubricants; this includes fluoroelatomers, which is found in engines and transmission systems. This will react with water to produce hydrofluoric acids which is highly toxic.
All crime Scenes should be dealt with in the correct manner to prevent the loss of any evidence which may be need later in court. The evidence colleted should be done considering the health and safety of everyone involved.
Reference
Class note, Graham Thompson, 2005
Melanie Pickthall Summer school: forensic and Crime Scene Investigation.
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