Crime Scene Investigation | Forensic Science Notes Part-1

Introduction

Crime, clues and criminals all three meet at one point that is the crime scene. It is the place where a criminal act took place. Thus it contains records of past events and is a starting point for the criminal investigation because it will establish and prove what happened at the time of commission of offence and will help to identify the criminal by the vital evidences found at this place.

Crime scene investigation is a long and tedious process that involves purposeful documentation of the conditions at the scene and the collection of useful evidence that could possibly illuminate what happened and point to who did it.

 The scene of occurrence can’t be limited to one place only. The number crime scenes may vary according to the mode of crime. There could be primary, secondary and often tertiary crime scenes. For instance, an offender might abduct at one location (primary crime scene), transport the victim (the car being a secondary crime scene), commit another crime at a distant location and then dispose off the body at a fourth scene.

Crime scene investigation

This can provide an opportunity to link suspect with the scene/crime providing proper collections and examinations are made of the scene, victim and suspect.

“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more bear mute witness against him. This is evidence that does not forget.

It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it can diminish its value.”

—Edmond Locard

Principle of exchange

Whenever two people come into contact with each other, a physical transfer occurs. Hair, skin cells, clothing fibers, pollen, glass fragments, debris from a person’s clothing, makeup, or any number of different types of material can be transferred from one person to another. To a forensic examiner, these transferred materials constitute what is called trace evidence. Some common examples of trace evidence include:

               • pet hair on your clothes or rugs

               • hair on your brush

               • fingerprints on a glass

               • soil tracked into your house on your shoes

               • a drop of blood on a t-shirt

               • a used facial tissue

               • paint chips

               • broken glass

               • a fiber from clothing

The first person to note this condition was Dr. Edmond Locard, director of the world’s first forensic laboratory in Lyon, France. He established several important ideas that are still a part of forensic studies today. Locard’s exchange principle states that when a person comes into contact with an object or another person, a cross-transfer of physical evidence can occur.

The exchanged materials indicate that the two objects were in contact. Trace evidence can be found on both persons (and/or objects) because of this cross-transfer. This evidence that is exchanged bears a silent witness to the criminal act. Locard used transfer (trace) evidence from under a female victim’s fingernails to help identify her attacker.

The second part of locard’s principle states that the intensity, duration, and nature of the materials in contact determine the extent of the transfer. More transfer would be noted if two individuals engaged in a fistfight than if a person simply brushed past another person.

Some examples of interchange between scene, suspect and victim:-

• blood – drops on floor, suspect clothing, etc.

• hair – pulled from victim or suspect.

• finger impressions – victim on suspect

• foot wears impression – suspect on the scene.

• soil material – from scene on suspect’s shoes.

• dust, dirt debris – from scene on the suspect’s clothing, etc.

• vegetation or flora – from scene on the suspect’s vehicle, clothing etc.

• material item (cigarette, watches, buttons) – suspect on the scene.

Crime scenes

It is the beginning point for obtaining evidence which will be used by the crime scene investigator and the forensic expert

A thorough investigation of the crime scene must be completed

What is a crime scene?

A crime scene is any physical scene, anywhere, that may provide potential evidence to an investigator. It may include a person’s body, any type of building, vehicles, places in the open air or objects found at those locations. “crime scene examination” therefore refers to an examination where forensic or scientific techniques are used to preserve and gather physical evidence of a crime.

The only thing consistent about crime scenes is their inconsistency. Because of their diversity, crime scenes can be classified in many ways. First, crime scenes can be classified according to the location of the original criminal activity. This classification of the crime scene labels the site of the original or first criminal activity as the primary crime scene and any subsequent crime scenes as secondary.

This classification does not infer any priority or importance to the scene, but is simply a designation of sequence of locations.

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