Thursday, May 31, 2012

Forensic Biology


COLLECTION OF BIOLOGICAL EVIDENCE.
The strength of any forensic evidence presented in a court of law highly depends on how effective its collection was and the sensitivity with which the evidence was handled after that. This previously ignored part of court proceedings seems to be catching up as evidenced with the professionalism witnessed in the police department lately.
Care is being taken during collection of this evidence just as required. Just to remind ourselves, biological evidence tends to deteriorate quite fast and get contaminated hence measures should be taken to prevent that and ensure its integrity.
The success in finding biological material depends upon the search method employed and also the integrity and state of the scene. It is important to adhere to the following guidelines while collecting the evidence:
  •      Wear the appropriate gear. These include full overalls, shoe covers, gloves and face masks.
  •       Seclude the area by marking it with tape to minimize human traffic.
  •       Start collecting evidence from outwards going inwards to capture as much evidence as possible.
  •       A range of light sources can be operated at fixed wavelengths and be used to detect stains.
  • ·   Take as many photographs as possible at different angles( Thats a whole topic all together)
Methods used for collection will vary depending on the type of sample. For example,
  •   Searching a crime scene or items recovered from a crime scene for blood can be aided by use of luminol (3-aminophthalhydrazide)The chemical can be sprayed onto a wide area and will become  oxidized and luminescent in the presence of haemoglobin, which is found in red blood cells. It is necessary to darken the area being searched in order that the luminescent are detected.
  •   Dry stains and contact marks on large immovable items are normally collected using a sterile swab that has been moistened with distilled water, in other cases scraping or cutting the material may be appropriate.
  •   Lifting from the surface using high quality adhesive tape is an alternative method for collecting epithelial cells.
  •   Liquid blood can be collected using a syringe. It can also be applied to FTA paper that is impregnated with chemicals to prevent action of microbial agents and stabilize the DNA.
  •   Smaller movable objects such as weapons, which might contain biological material should be packaged at the scene and examined in there controlled environment of a forensic laboratory.

TO BE CONTINUED…

Wednesday, May 30, 2012

Techniques in Making Shoe Impressions



Topic
Crime scene investigators make shoe impressions with plaster of paris and dental stone.
Introduction
The most common method of entering and leaving an area where a crime is committed is by walking. Criminalists often gain information by examining the surfaces on which a perpetrator walked. Footwear or bare feet can leave superficial prints on firm surfaces such as flooring.
However, walking across a soft surface like damp soil leaves impressions or indentations.
Footwear impressions can provide crucial clues in an investigation. Prints or impressions can show the points of entry and exit at the crime scene.
In addition, shoes carry materials from one environment to another. This material can provide information about where this person has been.
An impression can tell a lot about the shoe that made it. Every shoe is unique, with its own pattern of wear and tear. Therefore an impression of footwear can be compared to a particular pair of shoes to help connect those shoes to the crime scene. Impressions can also tell something about the height and weight of the wearer. Heavy individuals make deeper impressions than light ones. In addition, a tall person has a longer stride than a short person.
There are several techniques for making casts of shoe impressions. In this experiment, you will compare the effectiveness of two materials in making casts: plaster of Paris and dental stone.
Time Required
45 minutes on day 1
45 minutes on day 2
Materials
a)      2 pounds (lbs)(0.91 kilograms [kg]) of dental stone in a large
b)      Ziploc™ bag
c)      3 lbs (1.36 kg) of plaster of paris in a large ziplock bag
d)      3 to 5 cups of water in a bottle
e)      5 to 10 twigs or craft (Popsicle™) sticks soaked in water
f)        3 or 4 long strips of cardboard (about 4 inches [in.] by 24 in.
g)      [10.2 centimeters (cm) by 61 cm])
h)      large spoon
i)        talcum powder
j)        magnifying glass
k)      scrub brush
l)        paper towels
m)    access to water
n)      science notebook
Procedure, Day 1
  1.   Follow your teacher to an outdoor area where there are some shoe impressions.
  2.   Closely examine two footprints. Carefully remove any rocks, twigs, or other debris from the footprints.
3.   Sprinkle a little talcum powder over these two footprints to help hold the soil in place and secure the impressions.
  4.   Build a retaining wall around each impression using strips of cardboard (see Figure 1). 
(This wall will prevent the plaster of paris or dental stone from escaping when it is poured into the impression.)
  5.   Make a cast of one footprint using dental stone. To do so:
 a. Pour about 1 cup of water into the Ziploc™ bag of dental stone.
b. Knead the bag of dental stone for 2 to 3 minutes (min) to mix thoroughly.
c. Examine the consistency of the dental stone. Ideally, it should be similar to pancake batter. If it is too thick, add a little more water. (Be careful; if you add too much water, your mixture will be too thin.)
d. The dental stone becomes firm very quickly, so work rapidly to pour the mixture. Avoid pouring the material directly into the impression, which can distort it. Instead, hold the spoon just above the impression and slowly pour the mixture into the spoon so that it falls into the impression. When the impression is about half full, remove the spoon and pour the remaining mixture directly. The poured cast should be 2 to 3 in. (about 5 to 7.5 cm) thick.
e. Use a stick or pencil to etch your name and the date in the upper surface of dental stone.
f.   Let the cast sit for 30 min to harden. During this time, carry out step 6 below.
g. After 30 min or more, insert the handle of the spoon into the ground about 1/2 in. (1.2 cm) from the impression and gently pry up the cast.
h. The cast may have soil or grass on it; do not remove it at this time.
i.   Take the cast indoors and allow it to harden for 24 hours.
6.   Make a cast of the other shoe impression using plaster of paris. To do so:
a. Pour about 1 cup of water into the Ziploc™ bag of plaster of paris.
b. Knead the bag of plaster of paris and water for 2 to 3 min to mix thoroughly.
c. Examine the consistency of the mixture. Ideally, it should be similar to pancake batter. If it is too thick, add a little more water. (Be careful; if you add too much water, your mixture will be too thin.)
d. Pour about 1/2 in. (1.2 cm) of plaster of paris into the impression, using the spoon as you did earlier to avoid damaging the impression. Add some reinforcing materials such as twigs or craft (Popsicle™) sticks that have been soaked in water (see Figure 2). (Dry sticks will absorb water from the plaster of paris and make it brittle.) Quickly finish pouring the plaster of paris into the impression to a thickness of at least 3 in.
e. Follow directions e through i in step 5.
Procedure, Day 2
  1.   Examine each shoe cast. In your science notebook, note any significant differences in the casts.
  2.   Using a scrub brush, gently clean each cast with water. Pat dry each cast with paper towels.
  3.   Examine each shoe cast again. In your notebook, note whether or not washing damaged either cast.
4.   Closely examine each shoe cast with a magnifying glass. Search for nicks, cuts, or scrapes in the casts that indicate identifying markings on the shoes. Record these in your science notebook.
Analysis
  1.   Why might an investigator make casts of shoe impressions?
  2.   in your opinion, which cast was easier to pour, the dental stone or plaster of paris? Explain your answer.
  3.   Which material held up best to washing? Explain your answer.
  4.   Which material provided the most detail when viewed under the magnifying glass? Explain your answer.
  5.   Describe any nicks, scratches, wear patterns, or other unique marks found in either cast.
  6.   What information might a forensic investigator acquire from examining a shoe cast?
  7.   Complete a Venn diagram (see Figure 3) comparing the two casting materials.