How Crime is Detected and Prevented

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How Crime is Detected and

Prevented

In this essay I will describe and explain how different methods are used to detect and prevent crimes. The different types are Alcohol, Arson, Ballistics, Blood, Documents, Drugs, Explosives, Fibres, Fingerprints, Footprints, Glass, Hair, Paint, Plastic, Pollen, Soil and finally Teeth.

ALCOHOL: When a person is suspected of being under the influence of alcohol, the police can test them with different types of machines. These machines are called breathalysers. The Lion Alcolmeter S-L12 is the most common of these. These machines test the breath for traces of alcohol. If the suspect tests positive, they will be detained until they are cleared. Other ways of detecting alcohol on a person are physical tests. The police will ask the suspect to perform certain actions such as walking in a straight line and following a finger with there eyes.

ARSON: When the forensic gets to the scene he must be very careful. An arson attack would burn away most of the evidence so the forensic must be careful where he treads. They would look under furniture and cloth, as this would have protected any fingerprints or fibres lying there. One of the most important roles of the forensic scientist following an arson attack is to establish the chemical nature of the accelerant – the material used to start the fire. When the evidence has been collected, it is tested with acetone (propanone), which dissolves most accelerants. They can then be tested with chromatography to finds out what they are. If the compounds break down when being tested, infrared spectroscopy is used instead. This test however is not 100% fool proof. It can be incorrect.

BALLISTICS:  This is the study of firearms and bullets. When a modern gun is fired, the spiral on the barrel leave’s an imprint on the bullet. This can then be traced back to the make of the gun and even the gun itself. When the guns make is discovered it can be traced back to the shop it was purchased from and even the buyer. When a bullet is collected from a crime scene, it would usually be deformed of crushed from the impact. Forensics would usually test fire the suspected type of gun so that they could compare the results. This would give them a clear view as to whether it is the same gun.

BLOOD: Blood is of value in such crimes as murder, rape, assault, robbery, burglary and hit-and-run accidents. Blood evidence may aid an investigation by locating the crime scene, by identifying the weapon used, by proving or disproving a suspect's alibi, and by eliminating suspects. DNA profiling can be performed on any biological substance. It can also be used for the identification of bodies when samples from parents and/or children of the missing person are available. 

Blood and other body fluid evidence is rapidly decomposed microorganisms, so it is absolutely essential that such evidence is handled properly. To prevent cross contamination of samples, the disposable gloves worn should be changed often if they become soiled with a biological substance. 

  • Stains on clothes and fabrics: Any stain that is wet must first be air-dried. Each item is packaged separately in a paper bag, not plastic.
  • Stains on surfaces: Items to be checked for blood should not be dusted for prints. Whenever possible, the bloodstained item itself should be submitted for analysis. If this is not possible, part of the surface is removed. Body fluid stains can be swabbed using cotton buds dampened with distilled water. The cotton buds, along with control cotton buds – which have been used to swab a non-stained part of the surface – are air-dried before packaging separately in paper.
  • Samples from suspects: If blood, semen, saliva or any other body fluid samples are required from the victim, the suspect, or from anyone else, the samples should be drawn or provided in the appropriate colour coded tubes. Samples should be refrigerated, not frozen.

First an analysis must be carried out on a stain to determine whether it is blood or not - the appearance of blood varies greatly depending on the age of the sample, the weather and other numerous other factors. If it is, then the animal species origin must then be determined. Important information can be obtained from the size, shape, and distribution of blood splatters at the scene. Blood splattered clothing is packaged and taken to the laboratory. Detailed photographs are taken at the scene. Other body fluids providing evidence are semen, saliva, urine, and skin tissue. Conventional techniques can be used to analyse these, e.g. determination of blood group and comparison with medical records. Characterisation according to genetic factors is now the norm however, provided the samples are suitable, using evidence from the detection of certain enzymes and DNA profiles.

DOCUMENTS:  Ever since documents have been produced, people have been forging them. It is still used today, for adding extra’s to cheques, using a false name and many more. When a forensic is called to analyse the evidence he would use a variety of methods depending on the state of the document.

  • Identification of handwriting and signatures: This requires a comparison, using a microscope, of specimens of known handwriting from the individual concerned with the suspected forgery.
  • Identification of typewriters, photocopies and computer printouts: Individual characteristics of typewriters leave their mark on the documents they produce. A whole new area of the science is however evolving involving the machines that produce photocopies, faxes and computer printouts.
  • Identification and deciphering of indented writing: This involves looking at imprints left by a writer on paper underneath. The imprint can be looked at using different light sources, but the modern technique is Electrostatic Deposition Analysis (ESDA).
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  • Comparisons of inks and paper: Inks can be analysed for the pigments they contain, but more usually for the age of the ink. Paper has been traditionally examined with the microscope, but a revolutionary new technique, called the Video Spectral Comparator 2000 is capable of detailed analyses of both papers and inks.

EXPLOSIVES:

If a sample of powder is found, it is collected as if it is a drug. Samples of powder are collected in plastic bags or vials; liquids in vials. Plant material is submitted in paper bags, as enclosure in plastic bags will lead to decay.

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