Distinctive Features

1. Noadswood Science, 2012 Distinctive Features

2. Distinctive Features • To explain how distinctive features can be identified to solve a crime

3. Microscopes • Often evidence is extremely small to look at using the naked eye – microscopes help in analysing this evidence... • What types of evidence need to be studied using a microscope?

4. Microscopes • Any materials too small to be seen using the naked eye require the use of a microscope – this includes: - • Blood samples / body fluids / tissue / hair • Fibres (carpet / clothing) • Dust • Pollen / seeds • Soil • Paint • Glass fragments • Bullets • Money (fake)

5. Forensic Methods • There are many methods forensic scientists use to identify criminal involved in a crime, and many involve using microscopes…

6. Comparison Microscopes • A comparison microscope is used to compare things – it is like having two light microscopes together… • One bit of evidence is placed on one side, and another bit of evidence (the one you’re comparing it to) is placed on the other side • Looking into the eyepieces shows the two bits of evidence making it easier to compare the two (to see if you have a match)…

7. Comparison Microscope • Distinctive features allow forensic scientists to match evidence… • Fired bullets are unique to one gun, allowing crimes and guns to be matched – distinctive features include: - • Length of bullet • Shape and weight of bullet (calibre of the cartridge helping identify the type of gun) • Rifling marks on bullet (tiny imperfections inside a gun barrel causes scrape lines which are unique) • Other objects such as glass (bullet going through a window) and cloth (shooting through their clothing) can leave a pattern on the bullet (or even get embedded in the bullet)

8. Bullets • Look at the spent cartridges – this gives evidence of the type of gun used… Rifling Marks Shape & Weight Rifling Marks Length

9. Comparison Microscope • Distinctive features allow forensic scientists to match evidence… • Seeds can show where objects or people have been which can be used to back up an alibis or link individuals to a crime scene – distinctive features include: - • Size of the seed (length and width) • Colour of the seed • Shape of the seed • Type of seed Size Colour Shape

10. Polarising Microscopes Natural light (top) v polarised light (bottom) • Sometimes a light microscope does not show everything – polarising microscopes can be used which reveal extra details (these are regular comparison microscopes with polarising filters allowing observation of optical properties of double refracting materials such as crystals (polarised light vibrates with a specific direction whereas natural light vibrates randomly)) • Polarising microscopes are useful when looking at fibres and soil…

11. Polarising Microscopes • Distinctive features allow forensic scientists to match evidence… • Fibres are found at all sorts of different crime scenes (e.g. fibre from a burglar’s jacket on a broken window, human hair from an attacker etc…) • Fibres are not unique, but they can be used to link a suspect (or their clothing) to a crime and include: human hairs, animal hairs, clothing fibre, carpet fibre etc… Colour Thickness • *Polarising microscopes show the fibres in more detail, especially synthetic fibres Length Natural / Synthetic

12. Polarising Microscopes • Distinctive features allow forensic scientists to match evidence… • Soil is made up of minerals, water and organic matter and the soil composition varies significantly in different areas • Soil is useful for forensic evidence as it can show where someone has been (soil on the shoes of a suspect which matches a muddy field etc…) Colour • *Polarising microscopes show the soil in more detail, especially glass fragments and minerals within Size of particles Presence of unusual materials (concrete / glass)

13. Fibres • Look at the different fibres under the microscopes… • One has been found on the victim of a crime, and the other 3 come from potential suspects… • Which fibre matches the one found on the victim (and therefore potentially links a suspect to the crime)?

14. Electron Microscopes • Electron microscopes are extremely powerful – they use a beam of electrons to create an image displayed on a monitor • They can magnify 1,000,000x (light microscopes are around 1,000x) showing huge detail, though they cannot show colour and are extremely expensive! • Electron microscopes are used to look at layers of paint and pollen grains… Single molecule showing atomic bonding

15. Electron Microscopes • Distinctive features allow forensic scientists to match evidence… • Paint is applied in lots of thin layers – if forensic scientists know the colour and number of different layers of pain they can narrow down the make, model and age of a car the paint has come from (useful for car crashes / hit-and-runs as flecks of paint can be removed onto the victim’s car (or clothing)) Layers of paint Car body

16. Electron Microscopes • Distinctive features allow forensic scientists to match evidence… • Pollen grains can tell you a lot about where an object or person has been as different pollens are found in different areas • Forensic scientists look at the size, shape and surface structure of the pollen grains as each type of plant has distinctive pollen