Examinations, crime scene

Additionally, the laboratory may be required to maintain a capability of providing crime scene examinations. The forensic scientist must also be prepared to present expert witness testimony in court, and indeed a sizeable portion of time may be taken... 

During this time he experienced many complex and controversial cases, the vast majority of which were terrorist-related incidents. His main interests include the chemical examinations relating to firearms casework, research and development work arising from same, crime scene examination, health and safety issues, quality assurance, suspect handling and processing, and contamination avoidance procedures both inside and outside the laboratory. 

Trace Evidence. Trace evidence (23) refers to minute, sometimes microscopic material found during the examination of a crime scene or a victim s or suspect s clothing (see Trace AND residue analysis). Trace evidence often helps poHce investigators (24) develop connections between suspect and victim and the crime scene. The theory behind trace evidence was first articulated by a French forensic scientist the Locard Exchange Principle notes that it is not possible to enter a location, such as a room, without changing the environment. An individual brings trace materials into the area and takes trace materials away. The challenge to the forensic scientist is to locate, collect, preserve, and characterize the trace evidence. 

The newer applications involve the field of biotechnology. Proteins produced by genetically altered organisms such as bacteria must be examined to verify that they are identical to the same proteins produced by humans. Also, analysis of DNA from crime scenes is relatively recent. Indeed, DNA analysis and fingerprinting are powerful tools in modern forensics. 

Trace Evidence. Trace evidence refers to minute, sometimes microscopic material found during the examination of a crime scene or a victim s or suspect s clothing. Trace evidence often helps police investigators develop connections between suspect and victim and the crime scene. The challenge to the forensic scientist is to locate, collect, preserve, and characterize the (race evidence. 

The course on crime scene investigation will be offered by the College of Criminal Justice and will emphasize the importance of scene examination and evidence sampling. An improper sampling method can invalidate the results of the forensic laboratory. 

Physical evidence collected at crime scenes is sealed in special containers to prevent contamination and degradation and is catalogued carefully. A chain of custody is established and documented as the evidence is sent to a forensic laboratory. At the laboratory, the evidence is examined by personnel trained in one of several fields Forensic serologists examine body fluids, forensic pathologists examine human remains, firearms technicians classify and test firearms and explosives, and forensic chemists determine the composition and identity of materials. 

Forensic scientists examine evidence from crime scenes in an effort to solve crimes. This scientist is removing a piece of blood-stained material gathered at a crime scene for DNA testing. 

The fact that most samples examined are not pure substances, but are often mixed with dirt or debris, presents a major challenge to the forensic chemist. This may also be an advantage, as every substance collected at a crime scene is a unique mixture of chemical compounds that can ultimately be identified. Arsonists, for example, often use accelerants such as gasoline or kerosene to speed combustion and spread flames in the interior of a building. A forensic chemist may collect samples of burned and unburned materials, extract the volatile hydrocarbons, and separate the components for analysis by gas chromatography. 

It is most obvious that arson by electronics will be marked by seemingly mixed-up time and space relationships. The principal suspect may be discovered to be at a great distance from the scene of the crime. Polygraph examination may show that the accused has no actual knowledge as to when the alleged crime occurred. The suspect may be in the company of friends at the lime the incident takes place. He may be enroute to some distant point. He may have been absent from the locale for a... 

The chemical characterization of forensic evidence from a crime scene or the criminal has some different requirements from that of many other types of chemical analysis. High sensitivity is important because the quantity of material for examination is often limited to minute traces found at the scene. The material under scrutiny must be characterized as comprehensively as possible to ensure maximum discrimination from other material in the same class. Forensic laboratories are multiinstrument facilities required to deal with many types of evidence found at a crime scene therefore, the routine methods used should preferably employ relatively inexpensive instrumentation. In order to protect integrity, samples should be analyzed as received if possible and any workup minimized. The method should preferably not be labor intensive. Pyrolysis-gas chromatography (Py-GC) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) have proven to be an effective means of satisfying these requirements in many forensic science laboratories. - ... 

It is evident that Py-GC may be used to characterize many different types of material likely to be associated with a crime scene. It is a versatile and discriminatory technique that may be used for the forensic examination of materials by the following ... 

While on scene, avoid contact with any contaminated areas and avoid liquids or powdered materials. Persons fleeing from the event may be contaminated and should be isolated until they can be examined and cleared (Table 2.3). This should be the responsibility of law enforcement (in proper PPE), because terrified victims may refuse to obey EMS orders and may try to transport themselves to the hospital before decontamination. Preserve the crime scene as described in Chapter 1. 

Nowadays in the forensic science laboratory, large pieces of human (and animal) hairs collected from the crime scene are examined by morphological methods using macroscope, microscope, and electron microscope, and may be compared with sample hairs of humans associated with the crime. Finally, their origins are determined. 

However, it is well known that identification of hair by morphological methods is not always reliable and should be done by a well-trained analyst for maximum reliability. It is difficult to distinguish the suspect s hair from many other hairs left at the crime scene if there is no finding of particular characteristics in the morphology. Therefore, in addition to morphological examination, ABO blood typing from hair can be made, which is helpful in the... 

At the crime scene, various fibers and hairs are collected by policemen. They are immediately examined at the forensic laboratory in order to identify the suspect and help solve the crime. The examination needs to establish (1) whether it is a hair or a fiber (synthetic or plant) (2) its species if it is a hair (3) its somatic origin if it is a human hair (4) whether it is similar to the suspect or the concerned persons. Microscopic examination will resolve the first point. It will also allow discrimination between human and animal hair, as the medulla of human hair does not develop well and shows less than 0.30 of medullary index (ratio of medulla diameter to hair diameter). But determining the species of animal requires experience in animal hair examination. Almost every animal hair shows specific shape of cuticule and medulla under microscopical observation. With regard to the somatic origin of human hair, there are some basic features that usually indicate the bodily origin of the hair. For example, head hair has long length, 30-120 pm diameter, tapered tip, little diameter variation, various medullation, sometimes cut tips, and treatment. Pubic hair has a twisted... 

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