Potty
Mouth
Made for scientist
By scientists
The Art of Finger Printing
Collecting finger prints can be an extremely
important, if potentially tedious, process for a
criminal case. There are three methods depending
on the surface the print is on.
Non-porous surfaces: smooth surfaces where the
print lies on the surface such as glass, plastics, and
metal. These fragile prints need to be exposed to
superglue fumes, or cyanoacrylate ester which will
then be treated with a fluorescent dye stain so
you can view it under a laser.
Porous surfaces: surfaces that absorb the print,
such as paper, cardboard, and untreated wood.
Here, you need to use chemicals like DFO and
Indanedione to develop the print. Physical
Developer is used when the print has been wet.
Other surfaces: examples for this category include
adhesive tape, which you would need to use
sticky-side powder to lift the print and surfaces
that have been contaminated by blood, which you
would need to use Amido Black for.
Can You See It?
Hair and fibers can be a very important source for
DNA and can make or break a case. There are
three different ways to collect hair and fibers:
Visual: if the hair or fiber has different enough
coloring from the surroundings then it can be seen
without aid. You will then pick it up using clean
forceps, folding it into a clean piece of paper to be
sealed into an envelope or similar packaging.
Tape lifting: used usually with water or methanol
soluble tapes, this method is used for trace
samples that will then be packaged in a similar
manner as above.
Vacuum: the vacuum will have a filtered trap to
catch any trace in the suspected area but this is
not a commonly used option due to the danger of
cross contamination.
By the numbers:
Despite what crime shows like CSI might lead you
to think, collecting and processing evidence takes
time. Sending DNA through the system can take
up to two weeks, a little less if it’s a priority case.
What About Blood Samples?
Making sure you collect good blood samples is
important if you want to know exactly what
happened at the crime scene. Like with prints,
there are different ways to collect samples.
Cutting: you must use a sterile cutting device.
Wet absorption: You need to use a sterile swab,
gauze pad, or threads that have been wettened
with distilled, sterile water. The sample should be
collected on the same side; for example, if you’re
using a swab then you should concentrate on the
tip.
Tape: If the blood has dried sufficiently then you
can lift it with tape similar to lifting prints off of a
non-porous surface.
So What is “Time of Death”?
There are three different categories for time of
death. The physiological time of death is when
the body’s organs stopped functioning; this can
actually be several minutes after the deceased
stopped breathing. The estimated time of
death is the best guess at when the deceased
died based on the information provided by the
crime scene. The legal time of death is when
the deceased was found or pronounced dead
by someone else and is usually the time found
on a death certificate.
Watch Where You Step!
Footprints can be important evidence in a
criminal case as they can be used to help
determine sex, size, and weight of the person.
They are first photographed and measured and
you might take a plaster cast of it. These cast
molds are made by segregating the print or
similar indentation using a small frame and
pouring a mixture of plaster of Paris or dental
cement into the frame. Snow is especially
helpful for tracking and collecting footprints.
How Do You Determine Time of Death?
Again, there are a few ways to determine time of death.
One method is figuring out the temperature of the body
using the formula “37.5oC - 1.5oC”, which is the body
temperature minus the amount of heat lost per hour after
death. The body will continue losing heat until it reaches the
temperature of the surrounding environment, or the
ambient temperature. The most realistic reading is taken
from the liver since it provides a core temperature. Another
method is Rigor Mortis, the natural contraction and
relaxation of our body’s muscles after we die caused by
chemical changes in our bodies. Rigor usually starts
approximately two hours after death and will last for about
twenty to thirty hours, working its way down from the
smaller facial muscles to the larger muscles in the lower
body. Finally, Forensic Entomology can be used; by
determining at what point the insects are in their life cycle
and figuring out how many there are will give you a time
table for when the deceased died.