Forensic Science 4.4 Microscopic evidence

Learning outcomes Understand the distinctive features of trace evidence Know how microscopy can be used in Forensic Science

Microscopic evidence Many types of evidence are to small to examine Standard light microscope – not powerful enough Need better resolution Sharper image Scanning Electron Microscope Small as 10 nm 20x better than light microscope

Better and better Better contrast Improve contrast by: Clearer image Improve contrast by: Staining with coloured dye Polarising microscope – brightens object Comparison microscopy Bullet casings – which gun fired them? Striations

Why’s it useful? Trace evidence can link a person to a place Paint, pollen, dust, soil SOCOs use tape or suction to remove samples from clothes and upholstery Make up of dust is distinctive to certain areas – especially pollen

Pollen is the male gamete of flowering plants.

Apart from being useful to honey bees, it can be used by forensic scientists to link a suspect to the crime scene where a particular plant may be found growing.

Pollen grains come in all shapes and sizes…. … Pollen grains come in all shapes and sizes…. ….and they never decompose! Meaning forensic scientists can identify them on the remains of bodies from 100’s or 1000’s of years ago!

Mummy of Queen Hatshepsut

These pollen grains come from different species of borage or Forget-me-nots

These 2 green pollen grains are sunflower pollen.

This is grass pollen

This is oriental lily pollen