## Step 1 - Speaking

Speaking (and Reading)
What do you know about forensic evidence?
With your classmate, make a list of the following:

- Different types of forensic evidence
- How easy/difficult it is to collect
- What school subjects would be useful to be a forensic scientist.

Would you like to be a forensic scientist? Why? Why not?

Do the exercise.

Read about trace evidence and hair.

Teaching Tip: Find out about Forensics Almost every scientific field could be involved in forensics in some way. Here are just a few of the professionals who might work on a case: chemists, psychologists, pathologists (disease), botanists (plants), odontologists (teeth), entomologists (insects), and anthropologists (humans). So if you study forensics, you might use physics for comparing densities and investigating bullet impact; chemistry for identifying unknown substances, such as white powder that could be a drug; biology for identifying blood and DNA; and earth science for soil evidence. The foundational principle of forensics is that a person always brings something to the crime scene and always leaves something. Often this is in the form of trace evidence: hair, fibre from clothing, chips of paint or glass, residue, and other "traces" of who was there. Hair evidence is examined in a lab under a compound microscope. Experts look at the colour and shape of hair, but they also find out what stage of growth the hair was at in order to determine how it was left behind. At the last stage, it might have been shed naturally. But if the hair was at an early stage, it might have been torn out by hard physical contact. In cases of violent or suspicious deaths, a medical examiner looks at the victim. The examiner uses body temperature, the presence of bacteria, how digested the victim's food is, and other means to find out when the person died. He also looks for wounds or marks that suggest a struggle, and does an autopsy to examine the inside of the body as well. In cases where a death might be murder made to look like suicide, an investigator uses signs in the victim's body. In a drowning death, are there diatoms (microscopic water creatures) inside the body, from swallowing water? If so, do they match the diatoms found in the water where the body was? In the case of a burning, is there carbon monoxide, from smoke inhalation, in the bloodstream? If there is not, this would suggest that the person was already dead before the fire. Identification is essential for getting the right suspect, but each victim has to be identified, too. In both cases, fingerprints, birthmarks, scars, tattoos, bones, and teeth can be used. Although fingerprinting is often useful for nailing down a suspect, not everyone has had his or her fingerprints recorded, and the police might not have access to someone's prints. One method that is more useful than fingerprinting is dental imprints. Teeth marks made by a criminal or teeth from a dead body can be used for accurate identification, even if only partial evidence is left. The teeth or bite marks are compared to dental records, especially X-rays. After the 1995 Oklahoma City bombing, dentists were able to identify about 25% of the victims based on teeth recovered from the site. Prints All Over the Place Collecting fingerprints is not that hard to do at home. Some fingerprints are visible - you can see marks left on a surface by dirty or oily fingers. Dusting is usually used for this type. Other prints are latent - you can't see them, but there are marks left by sweat and other organic residue from fingers. Fuming is often used for these. If you have a magnifying glass, inspect your fingers. The unique patterns on your fingertips are caused by ridges in the dermis, the bottom layer of your skin. These patterns are fully developed in human beings just seven months after conception, while the fetus is still in the womb. The three typical patterns are loops, whorls, and arches. (Look at examples of different fingerprint patterns.) Your fingerprints are different than anyone else's, but did you know that fingerprint patterns tend to run in the family? If your fingerprints are a whorled pattern, one of your parents probably has a whorled pattern, too. It's just not exactly like yours! To dust for fingerprints, sprinkle talcum powder or cornstarch on dark surfaces and cocoa powder on light surfaces (like the outside of a drinking glass) where there are visible prints. You can use a small paint or makeup brush with very soft bristles to gently swipe off the excess powder and leave the print. Use clear tape, sticky side down, to lift the print and then stick it to an opposite-coloured paper. What kinds of patterns do you see? Who wrote it? Chromatography is used to identify different inks. Say someone committed a crime by changing the dollar amount on a check. Using chromatography, an investigator could tell whether more than one ink pen was used to write on the check and whether the suspect's ink pen could have been used. How does it work? Well, ink is not really made up of one colour: there are actually different pigments making up one ink. In chromatography, the ink is soaked in a solution so that the different pigments will "bleed" apart and the true colours be revealed. (As you might guess, there is a drawback: the evidence is destroyed in the process.) You can see how chromatography works by doing this experiment. Fill a tall glass halfway with water. Cut 3-4 strips of filter paper or of a heavy paper towel and attach the ends to a stiff piece of wire or a stick that can rest over the top of the glass. Next, make a large dot of ink about 1/2 an inch from the bottom of the strips, using a different brand of black marker, felt-tip pen, or ink pen for each strip. Set the strips in the glass so that the ends touch the water but the ink dots are above the water level. As the water soaks up into the paper, the ink will begin to separate into different colours. Note that some inks are not water-soluble; if the ink does not bleed, try using either nail polish remover or rubbing alcohol (stronger solvents that can dissolve the bonds in the ink) instead of water. You can also look at "suspect" paper itself - are there watermarks or imprints from writing on top? Professionals also study handwriting and can analyse a sample of disguised writing to see if it has characteristics that match a suspect's normal writing. Source: http://www.hometrainingtools.com/a/about-forensic-science-explorations-newsletter

Answer the questions.

1. Think of situations where different kinds of hair - not just human - might be good clues.
2. How might a medical examiner conclude that the person died before a fire?
3. Why is fingerprinting not always possible to identify a suspect?
4. Read here more about fingerprints: Fingerprint Analysis
5. Take your own fingerprints. What type have you got?
6. Read about chromatography. How reliable do you think it is? What are the disadvantages?

Discuss the answers with a classmate.