Clue 1 Magnetic Swipe Card
Introduction
The magnetic stripe on the stolen security access card can reveal the exact time the
culprit entered the crime scene. The card is encoded with a permanent PIN (Personal
Identification Number) on track 1 which is used to access personal information and
Track 2 is encoded with the time of day every time
1
the card is used. This time code remains
2
unchanged until the card is used again. Track
3
three is not used. Using the magnetic powder
supplied, you will establish the exact time the card
was used to break into the store room. You will
Track numbers on standard
magnetic stripe
then use a map of the Gold Coast to determine
which suspects had sufficient time to reach their
alibi and to commit the crime.
Equipment
Each group will need:
ƒ Magnetic Powder *
ƒ Gold Coast Map * (use a photocopy)
ƒ Sticky Tape
ƒ Compass or dividers
ƒ 4/5 sheets of white paper
ƒ Ruler with millimetre (mm) marks
*
Provided with the Evidence Kit – the powder is attracted to magnets but is not
actually magnetic itself and won’t damage the encoding on the card
L
VERY IMPORTANT NOTE: Be very careful with the magnetic powder – only a very
small amount is supplied but it is enough to conduct the test several times. Working
over a sheet of white paper to catch excess powder and spills will ensure the test
can be conducted more than once.
Procedure
Before you begin, review your Forensic Laboratory Code of Practice and ensure that
each group member is aware of her or his responsibilities (refer to the Job Descriptions
Wall Chart if necessary). Read ALL THE INSTRUCTIONS before beginning.
Step 1 – Determine time card was used
1 Evidence Officer Only: Collect the security
access card from the central store and record
all details of the transaction on the Chain of
Custody.
19 worksheets | clue 1 – swipe card
Chain of Custody
Name:___________________
Date:____________________
2 Make sure the card is clean and free of
smudges and fingerprints. Gently tap the
powder container to carefully sprinkle a small
amount of the magnetic powder along the
length of the magnetic strip.
IMPORTANT NOTE:
Only a small amount is supplied – to ensure clear results, make
sure card is clean before you start –clean fingerprints with
methylated spirits or water and a little detergent. Work over a
sheet of white paper to catch excess powder.
3 Being careful not to touch the magnetic strip,
gently tap the edge of the card over the paper
to shake off excess powder. Tap the card
against the table gently several times until
individual lines of powder appear as illustrated
on page 22.
4 REPEAT THIS STEP TWICE: the first ‘lift’ yields a
darker result – use the second lift for analysis
Carefully lay the card on the workbench (NOT
on a piece of paper). Lay a piece of sticky tape
on the stripe with the adhesive side down to
‘lift’ the code. Ensure the magnetic powder
adheres to the tape by carefully rubbing the
surface of the tape back and forth. Peel the
tape off the card and adhere to a fresh sheet of
white paper for analysis. Repeat with a second
piece of tape and use this for analysis.
5 Before continuing, carefully return the excess
powder to its container. Return the powder
and security card to the central evidence store
or pass over to the next groups’
Communication Officer (ensure each
transaction is recorded on Chain of Custody!).
Chain of Custody
Name:___________________
Date:____________________
6 Using the coding information provided on
page 22, determine the time the card was last
used and record the result in your note book.
Step 2 – Determine earliest possible arrival time
Now that you know the time the room was entered by the culprit, you can determine
whether each suspect had sufficient time to commit the crime and reach their alibi. In
order to do this, you will need to measure the distances between the crime scene and
each alibi location using the map provided. You will then determine the minimum
travel time required to reach those locations using some simple mathematical
equations.
worksheets | clue 1 – swipe card
20
1 For each suspect, you will measure and record
the length of each individual street travelled.
Use the map and a compass or dividers to
carefully step out small, equal distances (eg 3
or 4mm apart – keep this constant!).
Count the total number of increments (steps).
Next, multiply the number of steps by the
length of one increment to convert your
measurement to millimetres.
NOTE: Use the CENTRE of location markers
(round dots), or intersections between streets
as start and end points.
2 In your notebook, or on the whiteboard,
convert each measurement from millimetres to
kilometres using the scale provided on the
map.
3 For each street, road or motorway, you will
now calculate the minimum time required to
travel the distances you measured on the map.
You must use the average speeds provided on
page 22 to do this. You will need to rearrange
the equation given to calculate the time for the
measured distances and average speeds given.
(Hint: convert speeds given as km/hr to
km/minute first!)
4 Add the times you calculated for all the streets,
roads and/or motorways travelled to calculate
the total MINIMUM TRAVEL TIME to the alibi
location.
5 You can now check this time against the time
the crime was committed to determine which
suspect had enough time to commit the crime
and reach the alibi location.
Distance
Speed =
Time Taken
+
street 1
=
+
street 2
street 3 total travel
time
total travel time
crime
alibi
Discussion and conclusions
In the group discussion, discuss the results and consider which suspects are most
incriminated by your results. Consider the meaning of ‘average speed’. Does this test
alone provide sufficient evidence against any suspect? Is it impossible for any of the
suspects to have reached alibi locations in the amount of time between the encoded
time on the swipe card and the alibi time?
21 worksheets | clue 1 – swipe card
Time encoding
Use the information and sample time codes below to decode the card. The number of bars (thick, medium, and
thin) and the order in which they appear reveals the time. The space between bars is not important information
and does not need to be recorded.
TIME FORMAT AND SAMPLE CODES:
AM / PM
thick bars
(max: 2)
HOUR
TENS OF MINUTES
MINUTES
TENS OF SECONDS
SECONDS
thin bars
(max:12)
medium bars
(max: 5)
thin
(max: 9)
medium
(max: 5)
thin
(max: 9)
PM
2
4
:
7
2
:
4
< LAST MEDIUM >
< end of code >
THIN
seconds
MEDIUM
tens of seconds
THIN
minutes
MEDIUM
tens of minutes
THIN
hours
THICK
AM/PM
< BLANK >
PM 2:47:24
AM 8:34:13
AM
8
:
3
4
: 1
3
Confirmed information from police investigations
The following information was established by police during their investigations. Alibis were confirmed by
eyewitnesses whose names have been suppressed.
Suspect
Alibi Location
Earliest Confirmed
Time at Alibi
Route travelled to
Alibi location
Killing Heidi
Warner Bros.
Studios
10.45 AM
Parklands Dve Ö Olsen Ave Ö
Brisbane Rd ÖPacific M’Way Steven Bradbury
Dick Johnson
Racing (Stapylton)
10.35 AM
Parklands Dve Ö Smith St Ö
Pacific M’Way Ö Elliot Rd Ö
Jacobs Well Rd Mick Fanning
Burleigh Heads
10.20 AM
Parklands Dve Ö Smith St Ö
Gold Coast H’Way Adam & Wil
Gold Coast City
Council (Nerang)
10.40 AM
Parklands Dve Ö Olsen Ave Ö
Nerang-Southport Rd Charlie & Nicole
Coolangatta
Airport
11.25 AM
Parklands Dve Ö Smith St Ö
Gold Coast H’Way Average Speeds
Use these average speeds in your calculations. The speeds given allow for stopping / starting and typical midmorning traffic conditions:
30 km/hr
Parklands Dve .......................................................................... ________________ (km/min)
40 km/hr
Nerang Southport Rd, Olsen Ave .................................... ________________ (km/min)
45 km/hr
Brisbane Road, Gold Coast H’way, Smith St ................. ________________ (km/min)
55 km/hr
Elliot Rd, Jacobs Well Rd ...................................................... ________________ (km/min)
90 km/hr
Pacific M’way ........................................................................... ________________ (km/min)
worksheets | clue 1 – swipe card
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