Investigating a Crime CLU3M

Collecting Physical Evidence When a crime has been committed, the first job of the police is to collect all the evidence that they can find The careful collection, examination, and storage of physical evidence are a vital part of any criminal investigation. To protect the crime scene, the officers must accurately establish two boundaries: 1. The centre: the area in which the offence was actually committed 2. The perimeter: the areas surrounding the centre, where the offender may have been present or may have left evidence

Crime scenes are preserved for 3 reasons: 1. To allow for a thorough search of the crime scene. 2. To seize and collect physical evidence. 3. To ensure that the physical evidence is admissible in court. Contamination: the loss, destruction, or alteration of physical evidence

Forensic Science Forensic science is the use of biochemical and other techniques to analyze evidence It involves many different disciplines including alcohol, anthropology, chemistry, document identification and forgery, entomology, fingerprints, firearms, trace evidence, odontology, biology and pathology

Forensic Science A piece of evidence found at the scene of a crime will often be analyzed by several different methods to get the most information from it. I.e., a shoe may be examined for bloodstains (studied by biology, DNA analysis), trace evidence (broken glass or similar type of dirt found on suspects shoe and crime scene), gunshot residue (may be on suspect's clothes or hands as well) etc.

Impressions Patterns or marks found on surfaces and caused by various objects such as figures, shoes, tires, blunt objects, etc… Impressions have 2 characteristics: 1. Class characteristics: the general attributes of the object i.e. type of tire (Pirelli 15 inch radial) 2. Individual characteristics: specific and unique of an object i.e. tread wear on a specific tire

Fingerprints The unique patterned mark left behind after a fingertip touches an object It is unique to an individual and never change There are 2 types of prints: 1. Visible fingerprint: can be observed by the naked eye i.e. coated in blood or grease 2. Latent fingerprint: formed by natural oils and perspiration on the fingertip. Not visible to the naked eye.

Three methods are used to develop latent prints: 1. Graphite powder: used on non-absorbent surfaces i.e. metal plastic 2. Iodine fuming: used on surfaces such as paper and cloth 3. Laser beam: used to illuminate the print

DNA Testing DNA (Deoxyribonucleic Acid) - is the individual blueprint of a human being at a genetic level This is the newest of forensic science methods, as it was only developed in the 1980s. It is a very reliable way of linking an accused person to a crime.. can be found in the form of blood, seminal fluid, saliva, or skin. Once a person's DNA has been identified as the same as that found at a crime scene, there is a tiny chance that that person was not present, as only an identical twin would have exactly the same DNA.

Forensic Ballistics the science of analyzing firearm usage in crimes. Forensic ballistics involves analysis of bullets and bullet impacts to determine the type of firearm used. firearm and tool mark examinations also involve analyzing firearm, ammunition, and tool mark evidence in order to establish whether a certain firearm or tool was used in the commission of a crime.tool mark evidence

The Crime Scene Continued There are strict procedures on the seizure, handling, and storage of evidence: 1. no evidence is left unattended; 2. the case officer must secure evidence in the police property locker; 3. transferring evidence is the responsibility of the case officer; 4. no evidence can be removed from property locker without appropriate authority and signature. This is to maintain the chain of custody of the evidence.