18 December 2009
Encourage children to play detective and identify the thief who stole Mrs Callisto’s laptop with a series of science investigations
Don’t forget, subscribers can access the fantastic Interactive resource, ‘Whodunnit? The case of the stolen laptop’. This interactive crime scene will bring the investigations to life for children.
Conducting forensic investigations to solve a ‘Whodunnit?’ gives children a realistic context in which to make systematic observations and then draw conclusions. The activities that follow link to a fictitious crime committed in a school setting. You can use the crime scene Interactive resource, ‘Whodunnit? The case of the stolen laptop’ (subscribers only) – complete with Chief Inspector Hill, crime scene and suspects – to progress through the investigation, or use the downloadable Poster and Activity sheets (all readers).
The activities such as chromatography and the investigation of shoe scrapings for bicarbonate of soda could also be linked to work on changing materials.
Mrs Callisto’s laptop has gone missing. She had set it up in the staffroom to do some work after school and left it there for ten minutes – between 4.05pm and 4.15pm – while she went to get some resources from the science cupboard at the other end of the building. She had plugged the laptop into the mains and whoever took it unplugged the lead and took that, too. Fingerprints have been found on the socket. A security code is needed to get in and out of the building during out-of-school hours, so only members of staff had access at this time.
There are five suspects who were all on-site at the time:
- Mrs Starr – the Headteacher
- Mrs Garymede – the Chair of Governors
- Miss Halley – the Deputy headteacher
- Mr Neptune – a supply teacher
- Mr O’Ryan – the contract cleaner who was covering for the caretaker while he was off sick.
An anonymous handwritten memo has been pinned to the staffroom noticeboard that states:
Do not leave staff laptops unattended – or else
No one knows who put it there. Pens belonging to each of the suspects are available for analysis. The contract cleaner had sprinkled a deodoriser on the corridor carpet outside the staffroom, but this was not vacuumed prior to the crime being committed. Shoe scrapings will be tested for deposits of this powder. Each of the suspects has made a statement to police and had their fingerprints taken. (Note: All the evidence points to Deputy headteacher, Miss Halley, committing the crime. Why she stole the laptop is not part of the investigation.)
1. Shoe scrapings investigation
Learning objective: To recognise that vinegar reacts with bicarbonate of soda to produce a useful new material.
You will need: A ‘shoe scraping’ from each suspect (three: bicarbonate of soda and sand, two: just sand) labelled with each suspect’s name inside sealed plastic bags; vinegar; beakers; pipettes and Activity sheet 1, ‘Crime Scene Investigators: Shoe scraping analysis’.
Refer to the scene using the Interactive resource, Poster or Activity sheets, ‘Whodunnit? The case of the stolen laptop’ and ‘Setting the crime scene’ information, left. Explain that at the end of the school day, the contract cleaner always sprinkles deodoriser on the corridor carpet outside the staffroom. The deodoriser is then vacuumed, but on the date in question, this had not happened prior to the laptop’s disappearance.
Police believe that anyone entering the staffroom may therefore have traces of the deodoriser on their shoes. They have taken scrapings from all the suspects’ shoes and sent them to your class for analysis. (The cleaner, Headteacher and Deputy headteacher should all have bicarbonate of soda in their samples, while the others don’t.)
Explain that the ingredients of the carpet product include bicarbonate of soda that produces bubbles when mixed with vinegar. Explain that the children can use this fact to determine which samples contain deodoriser by mixing them with vinegar. Provide groups with samples labelled with each suspect’s name and Activity sheet 1, ‘Crime Scene Investigators: Shoe scraping analysis’. Discuss how the children will make their test fair – using the same amount of sample and vinegar for each test and observing them for the same amount of time. Emphasise that as police hope to use the findings as evidence, they must work methodically and not contaminate the samples. The children should carry out their tests by dropping vinegar from the pipette onto each shoe scraping and recording whether bubbles are produced. Check that every group’s findings agree.
While no two individual’s fingerprints are ever the same, they can generally be categorised as either loop, whorl, arch or composite. Loops are the most common fingerprint pattern. Share with the children (or click on the fingerprint icon on the Interactive resource) that the police found a number of fingerprints on the plug socket – composite and whorl (the cleaner and Deputy). Show children Activity sheet 2, ‘Crime Scene Investigators: Finger print patterns’ with examples of each fingerprint and compare these with those of the five suspects on the character cards. Who has composite and whorl finger prints? Are the children getting closer to solving the crime?
3. Chromatography investigation
Learning objective: To use chromatography on a range of inks and make observations about any changes.
You will need: Chromatography samples made with the thief’s pen (explain that this ink comes ready analysed by police forensic experts); five different ink pens – labelled with the suspect’s names; chromatography or filter paper; beakers; Activity sheet 3, ‘Crime Scene Investigators: Chromatography analysis results’.
If you haven’t already done so, use the Interactive resource, Poster or Activity sheets, ‘Whodunnit? The case of the stolen laptop’ and ‘Setting the crime scene’ information, left, to set the scene of who has stolen Mrs Callisto’s laptop? Explain that the children are going to investigate forensic evidence gathered at the crime scene. Also remind them of the anonymous note pinned to the staffroom notice board – could it be linked to the thief?
Demonstrate what happens to ink as water rises through chromatography paper and separates the constituent colours. Explain that different kinds of ink wash out in different ways, so that by testing the ink used to write the note and comparing it with each suspect’s pen, a match could be made. Decide, in secret, what pen will be linked to each suspect and ultimately which one will be Miss Halley’s.
Divide the children into five groups. Provide each group with a chromatography sample from the note (already prepared by you using the pen you want linked to Miss Halley); Activity sheet 3, ‘Crime Scene Investigators: Chromatography analysis results’; one of the five pens; beaker, and chromatography or filter paper strips. The groups should test each pen in turn using the chromatography or filter paper strips and compare the results to the sample you provided.
Discuss the results from each group, check everyone found a match for the thief’s pen and that they all agree who its owner is. Look at the character cards again and weigh up the evidence.
Bring all your evidence together and decide who stole the laptop. The children should deduce that:
- The shoe scraping investigation should have revealed that the suspects could only be the cleaner, the Headteacher and the Deputy headteacher.
- The finger print investigation should have revealed that the suspects could be narrowed down to the cleaner and the Deputy headteacher.
- The final chromatography investigation should have revealed that the thief is the Deputy headteacher.