Fingerprints

Basic Types of Fingerprints

 There are three (3) main categories of fingerprint.

A. Loops (70% of all fingerprints/ ridges flow to one side, loop around and flow back in the same direction)

B. Whorls (25% of all fingerprints/ ridges create a series of almost concentric circles)

C. Arches (5% of all fingerprints/ ridges run across, arch up, then flow back out the other side)

Within these three categories, there are more specific classifications.

A. Loops

1. Radial loops flow from the left.

2. Ulnar loops flow from the right

B. Whorls

1. Plain Whorls form concentric circles, sometimes almost a spiral.

2. Central Pocket Loops look almost like a whorl within a loop.

3. Double Loop Whorls flow across forming an ‘s’ pattern along the way.

4. Accidental Whorls look almost like a loop within a whorl.

C. Arches

1. Tented Arches are high and narrow, often with a singular ridge pointing up at the core.

2. Plain Arches are flat and broad, often looking almost like straight lines near the bottom.

 Pulling Prints

When pulling a print from a crime scene, it can be considered direct or patent, latent, or plastic. This classification depends on the surface the print is left on and the clarity of the print itself.

A. Direct Prints (also known as patent prints) are clearly visible prints left in a foreign material on a surface, like a bloody handprint. Because of their clarity, they are often photographed as opposed to lifted from the surface.

B. Latent Prints usually left accidentally and often contain a partial print if any at all. They are also often hard to detect in the first  place.

C. Plastic Prints are left in a material that holds the shape of the ridges such as wet clay or candle wax.

If a print is clearly visible, i.e. a Direct or Plastic Print, then oftentimes they will be photographed and entered into a computer via the picture, but Latent Prints almost always have to be lifted from the surface in order to be classified and matched to a suspect. Here are some methods.

Powder and Tape: Often called “dusting for prints” an investigator brushes carbon or aluminum dust lightly onto a surface,

Magna Brush: A magnetic wand that attracts iron is dipped in iron dust and brushed over a surface

Cyanoacrylide Fuming: Superglue is fumed over a surface, where the methyl- and ethylcyanoacrylate react with the amino and fatty acids as well as the proteins in the fingerprints and the moisture in the air, making the prints visible.

Ninhydrin: The ninhydrin liquid is sprayed, swabbed or dipped onto a surface, where it reacts with the amino acids in the prints and turning the prints themselves pink or purple.

Iodine Fuming: Iodine crystals are transformed into a gas and then wafted over surfaces, making latent prints visible for a short period of time.

Silver Nitrate: Silver nitrate is used to show prints on paper, mixed with water and applied to paper, it will react with the sodium chloride in human sweat and turn any prints black in light.

Amido Black: Amido black is used to develop prints in bloodstains by reacting with the protein in blood to turn it a blue-black color.