Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Forensics
In this exhibit you learn about how scientists can analyse evidence found at crime scenes to solve crimes.

In order to solve crimes and convict criminals, the police need evidence. There are many different types of evidence, and most come under the categories of witness testimony or physical evidence.

Physical evidence is more reliable than witness testimony, as witnesses can forget things, misinterpret what they see or hear or may even lie. Most physical evidence must be examined forensically to see where it comes from and what it means about the crime.

We can find out all kinds of things from physical evidence at a crime scene. Skilled forensic scientists can work out exactly what happened by the position of objects, such as working out how a pane of glass was smashed by the shape of broken glass and where it fell, or if a struggle took place by fallen furniture. They can also work out how long ago something happened by looking at things like dust or behaviour of insects.

Below: the back board, describing the crime and listing the evidence...
SCI-FUN Roadshow Exhibits -- Forensics : Back
The exhibit base board, with more information on the three forensic experiments, and the solution panel
DNA sample card from Exhibit #3
Fingerprint card, showing a print taken from the murder victim's neck: part of Exhibit #2.
SCI-FUN Roadshow Exhibits -- Forensics : Base
SCI-FUN Roadshow Exhibits -- Forensics : DNA
SCI-FUN Roadshow Exhibits -- Forensics : fingerprints

Criminals often leave evidence of their presence, which can be used to identify them. They may leave unique fingerprints or bite-marks. Their clothes may shed fibres, which can be used to identify their clothing. Handwriting, along with writing style, can be used to identify a criminal. Footprints can be used to identify the shoe size and type of the criminal, but also their weight and the way they stand and walk. And if their shoes pick up soil, the soil on their shoes can be compared to the soil at the crime scene.

Criminals often leave DNA evidence at crime scenes. DNA can be extracted from blood, saliva, skin cells, hairs, faeces and semen found at crime scenes. This can then be compared to a DNA database, or compared to DNA samples from suspects.

Other kinds of forensic scientists can study computers and identify which computer did something, and where that computer is. This is particularly important for solving cyber-crimes or crimes that have been organised using the Internet.

It is important to remember that forensic evidence does not always indicate that a person committed a crime, just that they were present at the crime scene.

When trying to convict a criminal, it is important that the police have as much evidence as possible. Under Scottish law, the prosecution must prove that the accused is guilty "beyond reasonable doubt". This means that a single piece of forensic evidence, or a single witness testimony is rarely enough.

1 Police need ________ to solve crimes and convict criminals.
2 Give three reasons why witness testimony is sometimes unreliable.
3 What can we learn from a criminal's footprints?
4 How do we identify someone from their DNA?
5 What must be proven in order to convict someone?
6 Why do you think it is important that crime scenes are not disturbed?

1 Dust for fingerprints. Take some dark coloured powder, such as ground up pencil lead, charcoal or pepper. Dip a soft brush into the powder, then lightly spread the powder over the area you want to dust (best to try a shiny surface). The powder will stick to the oily residue left by fingertips. Gently blow away any excess powder. Now carefully press a piece of clear sticky tape onto the print to pick it up. Stick your print onto a piece of paper.
2 Can you identify people by their handwriting and writing style? With a small group who know each other quite well, each of you write a secret note, planning a crime. Then fold all the notes up and jumble them up. Select the notes one at a time and see if you can work out who wrote them. Don't forget your poker face when your note gets read out.