CSI: Fingerprinting

NOTES - THEORY


Evolution:
Informant -> ID: photography, measurements, branding -> Fingerprinting (extraction) -> DNA fingerprinting


- French police Bertillon identified criminals through measurements:

• crown (circumference of skull)
• length of arm
• armspan

- Fingerprints quickly replaced this system.

• Latent - can be made visible with special techniques
• Paper
• Plastic

- Iodine vapour; fades and must be photograph
- Super glue fumes
- Dusting powder

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PRACTICAL PART 1

We did a lab practical to test the different methods of taking one's fingerprints. Unfortunately, I did not bring a camera...

Wood Glue Method

- Where are the pores found? Are they regularly spaced out?

- Are the lines of your print equally spaced throughout?

The lines on the fingerprint are not exactly equally spaced throughout, but they are of more or less the same distance. It was not easy to see the pores, because the fingerprint specimen was ruined in the process of trying to scrape the glue of our finger! (In our haste to finish the experiment, we had neglected to let the glue dry completely, and thus the print tore in 2 when we tried to take the semi-solidified glue print off our finger!)

Superglue Fuming method

- If the contrast of the white print against the black background is still too faint for a good detailed photograph to be captured, what could be done to enhance the fingerprint?

This is the answer I got from a website:

"This is the technique of dusting. Different colored dusts may be brushed onto the image of the fingerprint, and they will cling to the sticky white chemical from which it is formed, effectively changing its color."

http://www.ccs.neu.edu/home/feneric/cyanoacrylate.html

Iodine Fuming Method

 - What are the possible substances that may be used to render the prints more permanent?

- Why does the print disappear?

- Possible substances: Print is sprayed with a 1% solution of starch in water, which will turn the print blue and make it last from several weeks to several months. 

http://www.bxscience.edu/publications/forensics/articles/fingerprinting/f-fing03.htm

However, the most common is to take a picture of the print at its highest colour intensity before it fades. This is usually sufficient enough to determine the patterns of the fingerprint. The print disappears due to the fact that iodine sublimes (i.e. changes from solid to gas)


Power Dusting Method
Although my group members and I created a huge pile of lead shavings, we could either see only half of the OUTLINE of the print or nothing at all!


- What is magnetic powder dusting and how does it work?
A fine magnetic powder is held by a magnetic applicator, which may then be gently moved across the fingerprint. As no bristles touch the surface, this often damages the print less than other methods of developing the print. 
http://en.wikipedia.org/wiki/Fingerprint_powder

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PRACTICAL PART 2

Classification and Identification of Fingerprints

My own fingerprint database (it appears back to front because I didn't have a camera and had to take it with photobooth!)

The prints aren't very clear as I pressed my finger in the ink rather gently, but on the paper, they appear much clearer.

Class data:
Finger Pattern        213 Class Data/%
arches                   17.86
whorls                   28.57
loops                     53.57

According to the fingerprint database in the US:

• 60-65% are classified as loops
• 30 – 35% are classified as whorls
• 5% are classified as arches

The general trend is the same, with loops being the most common, followed by whorls and then arches. However, because we have a much smaller sample size, there seems to be a considerably larger number of arches as compared to the US data.

Questions:

- Are the patterns of your thumb print for the right and left hand the same?

- Are the patterns of the all of the fingers same, similar or different?

The patterns of my thumb print for both hands are different: my left print is that of a plain whorl while my right print is that of a right slant loop. The patterns of all the fingerprints seem to follow that of the thumb on each hand i.e. the other 4 fingers of the left hand are classic whorls while the other 4 fingers on the right hand are right slant loops.