"Who stole the Mars Bar?" Return to list of pracs

Aim: This project uses detective work of fingerprinting, soil tests and plaster casts to find the thief of a Mars Bar.

Worksheets:

• Fingerprinting;
• Plaster casting;
• Soil Testing;
• Forgery.

Story line: The forensic science project you prepare could include any of the following scientific investigations...

1. Chromatography with 4 different pens: cup, water, filter paper, 4 pens
2. Finger printing: glossy ceramic cup, baby powder, brush
3. Ransom note: finger prints, matching suspect finger printing.
4. DNA printing: from ransom note, suspects' blood sampling, fabric from scene.
5. Stain on fabrics: matching suspects clothing and victim with fabric dye (?).
6. Tyre tracks: Matching scene of crime with suspects' cars.
7. Indent on ransom note: imprint from sheet on top.
8. Soil pH sampling: from scene of crime and suspects' shoes.
9. Dental records: from victim, missing persons and known criminals.
10. UV light oil sampling: from clothing of suspects and victim.
11. Computer identification: match identity of suspect or witness ID at scene of crime.
12. Ballistics: puncture ID for 3 types of weapons at various distances to determine range of target killing and trajectory of bullet from victim's shirt.

Crime Scene: "Robbery of M&M's"

"When you return to school this morning you hear the tragic news. Someone stole the M&M's from your classroom early this morning. The room is always locked so therefore you suspect one of the teachers. So who could it be?"

Late last night after the students left to go home an evil and sinister crime was committed! Someone stole all the red M&M's from the lolly jay in your classroom. There was no obvious sign of break in and Police suspect an inside job. The lolly jar was tipped over and the lid was chipped. Evidence of blood remained on the jar and table top. The perpetrator ran through the vegie patch stepping in a pile of dog poo.

What evidence did Police discover?

a. Fabric from a shirt the perpetrator left behind on the fence of the school right near the classroom. Oil was found on it also and so samples were taken from the suspects clothing to try and match it also.
b. Tyre tracks over the fence near the classroom.
c. A ransom note with this warning

"Buy more red M&M's and deliver them to room ?? or else all the rest will go also and the lolly jar will be smashed."

d. The ransom note was written on a note pad on your teacher's desk. There is an imprint on it that held up to the light can be seen.
e. The ransom note has finger prints on it also.
f. The ink of the pen used to write the ransom note was tested (using chromatography) against pens confiscated from the 4 suspects.
g. The windows are normally cleaned every afternoon at 3.30pm but there were new finger prints on the glass in the door frame that Police believe the perpetrator may have touched.
h. Blood has been discovered on the door handle and on the chipped lolly jar lid. DNA has been collected from the suspects to match DNA.
i. Sample of dirt was discovered on the floor near your teacher's desk. Matching soil samples from the shoes of the suspects have also been taken to try and determine who stepped in the poo!

Suspect 1: "" the Cleaner : Having keys to go anyway throughout the school and having security clearance over night. He has been found to have a definite sweet tooth and is on medication for it. Doctors have prescribed 2 blocks of chocolate per week. He is also very fit and jumping a wall would be no trouble.

Suspect 2: "" Prep teacher : Known M&M addict suspected to be involved in illicit lolly dealings in her classroom. She has been known to bribe her students with M&M's in order for them to go out to lunch on time.

Suspect 3: "" Your teacher: d

Suspect 4: "" Office staff : Recently told by the Principal to stop eating the M&M's from the lolly jar and leave some for others, she is one of the most obvious witness.