Crime Investigations Unit

Some time ago (like a year or two) I downloaded and printed out a unit called "Crime Investigations: A Science Workshop for teachers in grades K-3" by Linda S. Hodges. Unfortunately I have no idea where I downloaded it from, and I can't seem to find the original either on the internet or on my computer. So you'll just have to take my word for it that's its great!! (I'd appreciate it if anyone comes across a link!)

I filed it away at the time because Billy was a bit young for it then, but knew it would be perfect for this 'holiday' week when I came across it again recently.

So over the course of 3 days, we put on our detective hats and tried our hand at crime investigation...

Analyzing tire tracks:

I gathered several toy cars with different tire treads on them (the Police car just came along to investigate - I'm not sure why the tank was there! :) ) While Billy wasn't looking, I ran one car over the ink pad and onto the worksheet to make tracks.

Billy then had to make the tracks of all the cars onto another sheet, examine them under the magnifying glass and note any uniqueness to the patterns. He measured the width of the sample and the tracks he'd made - that narrowed it down to 2 possible cars. He then had to examine them closely to determine which car had made the tracks.


After it was over he made up a story about all the different cars and the investigation, and filmed it on the video camera!


Investigating fabric samples:

Apparently the alleged criminal had ripped his shirt at the scene of the crime. I cut out 4 sample pieces + the unknown one from old white fabric in the rag cupboard. I think I used calico, t-shirt material and cotton.

Investigation involved examination under the magnifying glass, feeling the different fabrics and then dyeing them with red food colouring to examine how the different fabrics dyed in different ways.


A combination of the tests was enough to work out which fabric the unknown sample matched.



Taking & comparing fingerprints:

Using the ink pad and also rubbing our fingers on a sheet of paper where we'd rubbed a soft graphite pencil, we took our fingerprints. (We even took Pete's fingerprints as well). Billy then examined the fingerprints under the magnifying glass and determined whether we were arch, whorl or loop. We tried lifting fingerprints from a glass but were unsuccessful...


Doing chromatography on the ransom note:

Billy collected 3 different black textas from around the house, and I wrote a note using one of them on a strip of paper towel. He then had to draw a line on the other strips using each of the textas, and put each of the strips into a glass of water with the strip just touching the water. After a few minutes, the ink separated into its different colours and it was easy to match which texta was used to write the note. We tried initially using a couple of permanent markers and interestingly they didn't separate. It was a bit of a duh moment for me when I realised hmmm, that is probably the point of a permanent marker lol.


Billy wanted to expand on this one using different coloured textas - we saw this one at a homeschool meeting recently. So he set up another experiment using different colours.


Identifying foreign drink samples:

The criminal stopped and had a drink while he was at the crime scene and left behind a drink of an unknown dark liquid. I made up glasses with tea, coffee and pepsi and left them out overnight so they'd be harder to identify.

He started off by smelling them to try to identify the mystery drink. We decided tasting wasn't a good idea since it could be anything!, so then tested their pH. I was quite surprised to see how much more acidic Pepsi was than tea or coffee!

Once again we then expanded the experiment to test the acidity of orange juice and apple juice. (Both were still less acidic than Pepsi!)


Identifying foreign white powders:

We also found some white powder at the crime scene!

I made up bags to test with salt, sugar, plaster of paris, corn flour, bicarb soda and talcum powder. He tested a sample of each with vinegar to see if there was a reaction, then a separate sample of each with iodine. Finally he mixed the rest of the sample with water to see if it dissolved, what colour it was and whether the powder floated or not.


There was another unit involving lipstick smudges, but since I don't wear or own the stuff, we skipped that :)

It really was a good unit, and it was the ideal time to do it when we had a week at home without rushing out to other commitments. We only did 2 experiments each day which was more than enough for Billy's attention span - and mine too I have to admit! It took a fair bit of time to set most of them up, but it was quite enjoyable and something out of the ordinary!