Physical and chemical evidence BTEC First Diploma Unit 10 : Forensic science Name: Pawel
What is physical evidence?
Physical evidence includes:
marks and impressions such as footprints and tool marks,
trace evidence such as fibres, glass and paint
Physical analysis of blood can reveal what took place while a crime was being committed.
Shoe and boot prints are usually called footprints, although a bare footprint could have toe prints just like fingerprints. On hard surfaces, footprints of any kind can be developed and lifted like fingerprints. But impressions in soft material like mud can provide greater detail of the original shoe.
Even if a clever criminal has left no fingerprints, footprints or DNA, they may have used a tool when carrying out their crime. It might be a jemmy to force open a door or break a padlock, or even a weapon used to strike a victim or saw to cut up a corpse.
Fibres are easily shed or picked up. There are many different types.
They vary in cross-sectional shape.
Animal fibres such us wool are hairs which therefore have characteristic scales.
Window are often broken in burglaries. Car headlight are often broken in car accidents. Spectacles, bottles and glasses can be broken in a variety of circumstances.
They are thee different in types of glass:
Bloodstains can reveal an amazing amount of detail.
The pattern formed by a drop when it strikes a surface depends on size, direction and force.
blood dripping a short vertical distance will form circles.
What is chemical evidence?
Chemical evidence (e.g. paint, drugs) is a chemical which is left behind at the crime scene which can be analysed by forensic scientists to gain evidence.
There are different types of the chemical evidence like paper, gas or ink.
This type of analysis can be used to identify many chemicals, including dyes and drugs.
Gas chromatography and high performance liquid chromatography (HPLC) are in common use in forensic labs. Sample for analysis is placed in a vaporiser.
Paint fragments can be exchanged in car accidents and when burglars use tools. Paint varies in colour (pigments) an other chemical components, e.g. as in car paints and house paint.
Forensic toxicologists are concerned with substance that can caused harm to the body. They identify substance found at crime scenes or detect their presence in the body.