Quiz on reading.

Lecture.  Week 5.  Latent Fingerprints and inked fingerprints.

    A large part of the work of an evidence technician is looking for and collecting fingerprints; unfortunately, they are not often found.  The offender may have worn gloves, have poor ridge detail on his fingers or very dry hands, the latent prints may be smudged, or the technician may have bungled developing or lifting the print.  When latent prints are found, however, few pieces of evidence are as valuable.  Let’s start by defining some terms:

    A latent fingerprint is one that is not visible, but can be seen with the tools of the evidence technician.

    A plastic fingerprint is visible, three dimensional, and cast in a solid substance.  Think of someone pressing their fingertip in a smear of peanut butter on a counter.  More commonly, we would find these prints made in drying blood.  

    Another kind of visible print is the patent print.  Think of someone who dips their finger in blood and then touches a table.  This is like an inked print.  Do not confuse a fingerprint in blood (plastic) and a bloody fingerprint (patent)—they are distinctly different.  

    The fingerprint brush is usually made of fiberglass strands and is dipped in fingerprint powder.  The brush is swept across a hard surface to reveal latent fingerprints.  The fine black fingerprint powder sticks to the oils left behind when someone touches a surface with their friction skin.

    Friction skin is found on the hands and feet.  Look at the palms of your hand and see that the ridges cover the gripping side of your hand from the wrist to the tips of your fingers.  These ridges provide friction and help you hang on when you grab something.  The friction skin on the soles of your feet is a remnant of our early days when we walked barefoot.  We rarely find bare footprint latents, but if you ever do, they are just as unique and valuable as finger or palm prints.

    Your brush and powder are useful for revealing latents on hard, flat, dry, nonporous surfaces.  Lifting tape is usually used for preserving prints, but does not work well on porous surfaces like paper, pebbled surfaces like Formica or polished granite, or any surface with even the slightest trace of moisture.  There are other means of revealing and preserving prints on those surfaces, as described in the assigned reading.

    You will also be taking inked prints from another student and classifying those prints.  See HERE for instruction on rolling inked prints.

Reading Assignment for THIS week: 

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© Christopher Bruno