Processes of a Crime Scene Investigator
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Published: Wed, 04 Apr 2018
The main aim of my extended project is to find out what processes a Crime Scene Investigator goes through from the crime scene to court and how a forensic scientist analyses the evidence. The start of this essay answer this question, but then later on I will explain how my project developed and changed into a new outcome.
What processes does a CSI go through from a crime scene to court.
At the Crime Scene: Scene Recognition
When a CSI first arrives at the scene of a crime it is important that they start to develop an understanding of what took place at the location, before they start to retrieve the evidence. This is crucial as if they jump straight into the collection they could easily destroy some evidence. Other officials at the scene may also destroy or damage evidence unintentionally, so the CSI’s first priority is to secure the area in which the crime took place. This could range from just one room, to a whole neighborhood depending on how large an area the crime took place upon. For example if the crime was a car robbery, the crime scene may just be inside the car and the surrounding area, however if someone was murdered there may be evidence scattered around the vicinity, such as a blood trail. The core crime scene will be blocked off initially by the first officers that arrive on the scene; however it can be helpful to secure an area that is larger than the crime scene, so most CSI’s will block off an even larger area once they arrive. This is to ensure that all evidence linked to the investigation can be collected without it becoming tainted.
It is imperative that a CSI follows correct legal protocol throughout the examination of the scene, so once the scene is secure they may need to contact the local magistrate. This is because if the evidence is located in a place that is classed as someone’s personal property, such as on their body or in their car or house, they have the right to refuse a search. With a warrant present the officer can search the area without permission; it also means that its admissibility cannot be questioned as easily in court.
Once a search warrant has been obtained the CSI can begin their initial walk through of the scene. This is where they follow a pre-decided path either through or around the scene. The path is chosen based on where evidence is least likely to be, so that there is as little disturbance of the scene as possible. During the walk through they take notes on details that will only be present for a limited time, these can be things such as what can be smelt, what can be heard, what are the conditions, such as temperature, weather and time of day, and are there any potential hazards which need to be addressed immediately.
Once they have gaged the scene, they decide whether they need to contact specialists or get any specific equipment, for example if there is blood spatter on the ceiling it can be easier to for an expert to analyses it at the scene, rather than to deliver a large section of the ceiling to the laboratory. During this time they may also take time to talk to the first responders, to find out if they touched anything at the scene and to gather anymore information that may be useful whilst analyzing the scene. Also if the detectives have begun interviewing witnesses, they may also offer some more advice as to where may be the best place to look for evidence first. Most CSI’s do not talk to witnesses as they deal with physical evidence.
All the information that is gathered helps the CSI to develop a logical approach and form a plan as to how to collect the evidence and in which order, but first they must document every aspect of the scene. This is called the scene documentation stage or the second walk-through.
At the Crime Scene: Scene Documentation
The main aim of scene documentation is to create a record of how they scene appeared visually at the time of arrival. This is so that the forensics lab and the prosecution team can understand what the scene looked like, even though they may have never been there. To do this the CSI uses a range of equipment such as a sketchpad, graph paper, pens, pencils, measuring tape, rulers and a note pad so that they can accurately draw a representation of the scene. The most detailed form of representation is by drawing a sketch of the scene. This can include specific details that can be important to the case, such as room dimensions, locations of important evidence and pathways that may have been taken through the house. This is important so that we gain an overall view of what may have taken place at the scene and in which order.
As well as drawing sketches, they must photograph the scene using a digital or film camera with a range of different lenses and filters. They must do this before they touch or move anything so that they have an accurate representation of how the scene was left after the incident. These are less accurate than sketches when representing the location of items as it can be hard to display numerical distances in photos. The CSI must ensure that they take a range of photos from close up shots, to long shots, so that they have a range to use as evidence. Long shots show the exterior of the crime scene or the view of an individual room from one corner, whereas close up shots show individual pieces of evidence. All photos that are taken must have a number included in the picture, and then be recorded in a log. The CSI must log each photo that they take and then include details such as the photograph number, the date and time, the location and a description of what is in the photo.
To accompany the photos, especially in a case that takes place over a large surface area, a video may also be recorded that will involves full a walkthrough of the scene. This can help give a better understanding of the layout of the scene, as it includes details such as time distances between certain locations
Detailed notes must also be written at the scene, which include all details of the CSI’s observations. It is paramount that they remain objective whilst writing notes and that they stick to clearly stating the facts, rather than forming conclusions before scientific proof. For example if there is a pool of a reddish liquid surrounding a body, they must state that it is a reddish-brownish liquid, and not blood because it may be some other substance which has a similar appearance to blood. Once all the documentation is complete the CSI can begin to determine how and in which order they are going to process the evidence.
Examining the scene
Before ploughing straight in, the CSI must decide which pattern of evidence collection they are going follow. By following a strategic pattern, it ensures that all areas of the scene are analyzed and that nowhere is missed out or forgotten about. This is important so that evidence if collected effectively and no evidence gets damaged during the process. There are many different methods that can used to search different types of scenes but there are 5 that are used on a main day-to-day basis.
- Inward Spiral
- Outward Spiral
The parallel search involves a team of CSI’s forming a line against one side of the scene and working their way across the scene whilst staying in their parallel lines. It can also be done by one individual if they start in one corner and keep repeating the process a little further along the boundary each time, till they reach the parallel corner from where they started.
A grid search consists of two parallel searches, one in the horizontal direction and one in the vertical direction. This method is more accurate than a parallel search as the scene is searched more thoroughly, meaning that it is likely that more evidence may be found.
During a zone search the scene is divided into different sections, which are each numbered for a reference. Each zone can be searched by a different CSI, so the search is completed much faster, or a single CSI can search each zone one at a time. If multiple CSI’s are searching different zones, after the first search they may swap round so as to ensure that the area has been search effectively, and that nothing has been missed.
The inward spiral and outward spiral both follow the same principles, just in different directions. During the inward spiral process the CSI starts at the perimeter of the scene and works their way inwards, towards the center of the scene. However during an outward spiral, the CSI starts at the center of the scene, and works their way out towards the perimeter. Both of the spirals can be performed clockwise or anti-clockwise depending on the scene and the CSI completing the search. When completing the search the CSI must remember to look at the scene from all angles as different shadows may help to display more evidences that may have otherwise been missed. They must also make sure they remember to look up as the crime scene will be three dimensional.
At the Crime Scene: Finding the Evidence
When all of these processes have been completed the CSI can begin to collect the physical evidence. Throughout the process they must find, collect, and then correctly package all of the evidence so that it doesn’t get damaged during transportation back to the lab. This is important as it may need to be examined in court if it links a suspect to the crime. There are five main types of evidence, which are: trace evidence, impressions, body fluids, weapons/ firearms and documents. These can all play an important part when identifying what took place at the scene and who was involved.
There are 5 main categories of evidence that a CSI will search for though-out the crime scene. These are:
- Trace Evidence
- Body Fluids
- Questionable Documents
For each of these different categories the CSI will implement a range of different techniques to recover the evidence.
Weapons may be the first item collected at the scene, so that they do not cause harm to any of the officers on the scene. Weapons come in a range of
When weapons are used it can leave behind an impression. ‘Impression evidence includes any markings produced when one object comes into contact with another, leaving behind some kind of indentation or print. Common such evidence encountered includes footwear impressions, tire marks, and markings created by tools and similar instruments.’ (http://forensicsciencecentral.co.uk/impressions.shtml)
When tools or weapons are used in a crime more often than not marks will be left behind. There are two categories that frequently used tools fall into, cutting instruments and levering instruments. Cutting instruments are items such as a knife, saws and cutters, whilst levering instruments are items such as screw drivers or crowbars. When these instruments are used it is often with force. This means that a distinctive pattern or indentation can be left at the scene. This pattern can be cast using a silicon rubber. The cast can then be analysed and linked back to the object that caused them, hence linking a suspect to a crime.
Footwear impressions can be 2 or 3 dimensional and link people to the scene of a crime, as each time someone takes a step they may have left an impression behind. 2D impressions can be lifted in a similar way to fingerprints by using chemicals, dyes and fine powders. 3D prints can be created when someone steps on a soft surface, such as soil. A frequently used method of recovering 3D prints is to create an impression using a casting material such as plaster of paris. When the mixture is poured into the impression it hardens so that it can be removed and then analysed.
Impressions can be very delicate so have to be handled carefully, especially when they are in dust. These types of impression can however be lifted using electrostatic treatment. This involves placing a thin layer of conductive film over the impression, then a voltage is passed through it, causing the particles to jump onto the film. This results in an image of the impression left on the film, which can be used for comparison. Impressions in snow can also be very delicate, so in this case Snow Impression Wax is used. It is applied to the impression multiple times every couple of minutes and then left to dry. Once dry it can be cast like any other 3D impression.
Footwear impressions can carry a large amount of information with them as different under soles have distinct patterns. These patterns can be linked to a specific brand of shoe, and a specific individual as different shoes have different degrees of wear. This is because when someone wears the shoes, specific damage can be caused depending on the way in which they walk. If there is a suspect, a sample of their footwear can be obtained, and compared to the impression left at the crime scene. Due to the specificity of different shoes, if the suspects shoe impression matches the impression left at the scene, they must have been there.
Tire impressions can also link a vehicle to a scene, just like a footwear impression links a person to the scene. If a vehicle has drove over a soft surface at the scene then an impression can be left of the tyres. These can be lifted in the same way as footwear impressions and then compared to the suspect’s vehicle. If a vehicle is linked to scene it can then be examined in the same way you would examine a location, to see if there is any evidence present.
As well as footwear impressions, a suspect can be linked to a crime scene using their fingerprints. The human skin is made up of 3 layers which each come together to form a pattern of ridges and furrows, which are your finger prints. They are fully formed by the time you are 24 weeks old, as they develop whilst you are in the womb. The pattern of ridges is determined by how much you moved around when you were in the womb, and this explains why everyone’s fingerprints are completely unique. Each ridge contains a row of pores, through which we sweat. This is why when we touch a surface the pattern of ridges is left behind.
Even though everyone has completely different finger prints, they have been categorised into seven different shapes.
- Central Pocket Loop
- Double Loop
- Plain Arch
- Tented Arch
- Plain Whorl
Loops are categorised by a ridge that crosses from one side of the pattern, loops around and exits on the same side. Whereas an arch is a ridge that enters on side of the pattern and exits the other side.
Fingerprints that are left at the scene of a crime can be found in three forms, visible, plastic or latent. Visible prints are those that can be seen because they have been left in a dried substance such as paint. Plastic prints can also be seen but are in a soft surface, such as putty and latent prints are left by sweat and other oils on the skin, and cannot be seen without treatment. For a latent print to be recovered for comparison and analysis it needs to be treated. The method in which it is treated depends on the surface that it has been left on and the environment. If the print has been left on a non-absorbent surface, the most common method of collection is using powders or fuming.
Once the CSI has decided they are going to powder a print, they must next decide which method they are going to use, and which powder. There are many different forms of powder that are all used for different situations and for against different colour backgrounds. For example the black powder may be used to develop a print on a light surface, but you may have to use a fluorescent powder against a darker surface. Alternatively the CSI may choose to use a Magna brush with a magnetic powder. This is more accurate than using a brush as there are no bristles so there is less chance of the print being smudged or overdeveloped. If either of these happen the print cannot be used as it is damaged. To develop a print a very small amount of powder is placed on the brush, which is then gently swept across the print. The powder sticks to the body oils that are in the print, making it visible.
Once the print has been powdered, it can be lifted using clear tape. The tape is carefully placed over the fingerprint; this leaves an imprint of the fingerprint on the tape. The tape is then placed on top of a plastic cover this preserves the print so it can be transported back to the lab for analysis safely. Once back at the lab the print can be scanned and converted into a digital image which can be used for comparison.
Another method that is commonly used is the application of ninhydrin or triketohydrinene. These react with the amino acids that are in the print to produce a purple colour. Once the colour has developed, around two hours after application, the image can be lifted like a powdered print.
A more complex method is the fuming method, which can be done using either superglue or iodine crystals. This has to be completed back at the lab as it involves heating the substance so that the vapours combine with the print, making it visible. The print has to be photographed immediately as the image only lasts for a limited amount of time.
For a print to be linked to a suspect in court it needs to be analysed by two CSI’s. If they both match the collected print to the suspects print, then the suspect must have been at the scene of the crime.
Why I chose to research Forensic Science
Due to the soar of television programs around the subject of crime, the job of a CSI can often be confused between reality and what we watch on TV. The role of CSI’s and a forensic scientist is very important as they perform many tasks that are important in today’s society.
Recent examples of CSI
Interesting to others too
Through-out my research I have continuously discovered a range of fascinating facts that I didn’t know before I set out on my project. This made me realise that due to popular TV series such as CSI and silent witness, there are many misconceptions around how the process of Forensic Science actually takes place. I feel that due to its importance in today’s society, it would be a great idea for me to share some of my knowledge with others as I am certain that they would find it as fascinating a subject as I am.
This prompted me to find a way to educate others about Forensic Science so when the opportunity arose for me to run a weekend cub scout camp, with a theme, I jumped at the chance. The first thing I had to do was come it with a suitable programme. This meant that I had to decide carefully which out of all the topics I could cover would be the most education and interesting to the cubs.
The first topic I decided to defiantly include was fingerprints. This was my first choice as I had already done some quite detailed research into the different types and shapes of prints but also because I knew I could involve some fun activities into the session. I started by teaching them how are fingerprints are developed
Planned a course for students to learn from my research
Ideas for future
In the future I hope to continue developing my understanding of Forensic Science and Crime scene investigation and I believe that the degree that I will be studying in September will quench my thirst for this. Also I would like to continue teaching others using the knowledge that I have already gained, as the weekend away proved to me that many people out there don’t have a true understanding of what Forensic Science actually is, and that many people other than myself see it for the fascinating and intellectually exciting subject that it is.
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