Do It Yourself Detective is chock-full of fun forensic activities to try at home. From fingerprinting to blood spatters, there's something here for everyone. Make sure you get permission from whoever's in charge first though... these experiments can be messy!
- Chocolate Fingerprints
- Casting Call
- Bleeding Marvellous
- I Spy Fibre...
- Make an Impression
- Planet Science - CSI
You'll be a dab hand at detecting by the time you've finished this fun fingerprinting game!
>> What you’ll need:
- Fingers + friends fingers
- An assortment of drinking glasses
- Cocoa powder
- A small artists brush
- A magnifying glass
- Inkpad
- White paper - one sheet per person
>> What to do:
01. Give everybody a glass and a sheet of paper.
02. Make sure the glass is clean and has no marks on it.
03. Get everybody to make a finger or thumb mark on the rim of the glass.
04. Once they’ve done this, the detective work starts. Swap glasses - being careful to touch only the base of the glass. Don't smudge the prints that are already there!
05. Examine each glass for fingerprints. Using the brush, place a small amount of cocoa powder over where the prints were made.
06. Use the brush to lightly dust over the prints to help make them a bit clearer.
07. On sheets of paper get each person who left a print originally to make another print - but this time they have to press their finger or thumb in the inkpad first.
08. Match these new prints to the ones you dusted for earlier. Use the magnifying glass to help you inspect them even more closely and try to match them up.
10. See if you can name the 'culprit' who left their prints on each glass. When you've had enough, wash the glasses and start again!
>> What’s Happening:
No two fingerprints are the same, even twins will have differences in their prints.
When you examine a print you'll notice the lines occur in one of three characteristic patterns, known in the biz as 'arches'. 'loops' and 'whorls'.
When you come to compare the chocolate and the ink prints you should get an exact match between pairs. But although two different people may have the same fingerprint type (eg. both have loops on the same finger), there will always be other little differences between individuals. That's because it's not the shape of the print that’s unique, but rather the number, location and shape of specific ridge characteristics...
What you were lifting with the cocoa powder are called 'latent' prints. These prints are formed by oil and sweat from a person's fingers when they touch a surface - the sweatier you are the clearer they’ll be (so remember to wash after being sweaty)! They're invisible to the naked eye, which is why they need some kind of treatment to help you see them.
And from fingerprints... to footprints.
If you want to make a big impression, try this fab footprint-identification exercise!
>> What you’ll need:
- A shoe or foot
- A plastic container, about the size of a shallow ice-cream tub.
- Plaster of Paris
- Mixing spoon
- A mixing bowl
- Enough moist sand or moist soil to cover the bottom of the container
- Rubber gloves
>> What to do:
01. Put the gloves on before handling the soil or sand. Place the sand or soil into the plastic container.
02. Make an imprint of your shoe, foot or hand in the damp sand. (If you mess it up, just smooth the sand back over and try again.)
03. Mix up some plaster of Paris - read the pack for instructions until it's got the consistency of thickened cream.
04. Pour the plaster mixture into the footprint impression. Top tip: when you've finished, make sure you wash your mixing container and mixing spoon while the plaster is still wet...
05. Leave the plaster for about an hour and a half to dry. It’s best to leave it for this amount of time, because although the outside may appear dry and hard, the underside may still be wet and soft.
06. Once the plaster is dry, remove the cast from the sand. Gently brush off any excess sand.
07. Examine your imprint. Show someone else the cast and a range of shoes. Can they work out which one made the print?
>> What’s happening?
The plaster sets inside the imprint of your shoe, making a perfect copy of the track. This means a forensic expert could look at the track and match it up to sole of the shoe of any suspects either eliminating or incriminating them.
There's a lot of fun - and science - to be had investigating the way liquids spatter.
>> What you’ll need:
- Red food colouring or artificial blood (you can buy this at a fancy-dress shop or make your own with our Halloween special!)
- Dropper
- Small beaker
- Plain Paper
- Ruler
- Metre rule
>> What to do:
01. Lay out some paper to protect the floor, then place the paper you’ll drop the blood onto on top of them.
02. Hold the dropper 10 cm above a clean sheet of and drip one drop of blood onto the sheet.
03. Measure the distance of the spatter, making sure to write down the height it was dropped from and the diameter of the splatter.
04. Drop the blood from 20cm higher each time until you get to 200cm or higher if you wish (you can go up in larger or smaller amounts depending on how much time you have).
05. Measure the diameter of the spot and write it down as well as the height it was dropped from.
06. Use a new piece of paper to drop the blood on every time you change height (this will avoid confusing results).
07. Make sure you’re measuring the distance of the splatter each time you drop the blood.
08. Once you’ve done this, get someone else to do a splatter at a distance of their choosing (it can be any height within the range of the distances already dropped i.e. 10cm to 200cm).
09. Make sure whoever conducted the test originally can’t see the random drop, because their task now is to work out what height it was dropped from by measuring its splatter and comparing it to their results from before.
10. If they have recorded their results accurately, then they should be able to guess what height the random drop was dropped from.
>> What’s happening:
This type of forensic analysis is called Bloodstain Pattern Interpretation, but we’re going to call it Blood Splatter. What we’re trying to do is re-create the circumstances in which a crime may have been committed.
Once you know about the different ways that blood splatters, and can recognise certain signs, you can begin to work out what happened. It does require some specialist training though.
The specialist will try to determine what the position and shape of the spatter indicate. They take measurements to determine the trajectory as well as carrying out carefully controlled experiments.
These experiments will use materials very similar to those found at the scene, because blood reacts differently depending what surfaces are involved. For example it will behave one way when it hits a carpet, and another when it hits a tiled floor. Using the results of the experiments, investigators can try to reproduce what has happened.
Every item that touches another leaves a trace of itself behind. Can you match crime scene fibres to their original samples?
>> What you’ll need:
- Microscope
- Patches of fibre: such as cotton. linen, silk, wool, polyester, nylon
- Another separate patch of one of the above materials
>> What to do:
01. Look at each fibre in turn and study them closely, making sure to note down any special characteristics that each one has.
02. It’s important that you know for certain what each patch is, so you may want to write the name of the material on each patch, except for the separate mystery patch (just make note of what it is on a piece of paper and keep it hidden away).
03. Secrecy is the key, because the idea is to look at the last piece and get the others to work out what fibre it is from the notes they made earlier.
04.When the guesses have been made, then it’s time to reveal what the mystery material is...
>> What’s Happening:
The characteristics of many fibres are such that once you get to know what your looking it, you’ll find them easy to spot. To help here’s a guide to what sort of things you should be looking for.
Cotton is a flat and twisted ribbon-like fibre, it appears to be thick and rounded along the edges. That’s because each fibre is a long and twisted tube.
Linen looks like a tube with walls thick enough that it does not collapse, unlike cotton, which appears ribbon-like. Look for frequent small knobs. A narrow line in the centre is also dead giveaway.
Silk is solid like a thread of solid glass. Its diameter is the same all the way through it.
Wool is different from any other natural fibre, it looks broken or scaly under magnification.
Polyester has borders that aren’t regular or smooth but have a granular look. Small lumps of material sticking out from the fibres causes bits to pull together after a while and snag.
Nylon is pretty similar to silk but nylon is twisted in a spiral, unlike the straight threads of silk.
By identifying a piece of fibre at a crime scene, you could then potentially link it to a suspect who might have matching fibres in or on the clothes they were wearing when the incident happened.
People have been sent to prison on the evidence of fibres found at crimescenes. You might call it material evidence… (or you might not).