Rachel Way
June, 2007
Forensics Event Hints and Explanations
a) Powders:
-General:
-sometimes they don’t provide you with all of the materials they say they will, so know alternate methods of identifying them
-States/Nationals:
-know what they are AND what they do
-example question: Suspect A was depressed; it is your job to have identified that powder AND know which powder is an antidepressant
-at this level, they rarely tell you what powder is associated with each person, but rather they will tell you a condition about this person (like depression or diabetes), and you need to match them up with the powders that have been identified
b) Polymers:
-General:
-know the resin codes and uses for each type
-Regional/States:
-be able to identify actual samples of plastic
-example: you will be given a Styrofoam peanut or pieces of a cut up plastic bag
-Nationals:
-you will have to do a density test
-no actual samples are given
c) Fibers:
-General:
-know which fibers are synthetic and which are natural
-know what each type of fiber is generally used for
-example: cotton is used for towels, nylon is used for parachutes, silk is used for velvet etc.
-my suggestion for identifying fibers
1) feel the fiber
-if it’s stretchy, it’s spandex
2) do a burn test
-if it burns and has no smell, it’s cotton or linen
-if it burns and smells like burning hair, it’s wool or silk
-if it melts and it isn’t spandex, it’s nylon or polyester
3) use the microscope to distinguish
-cotton vs. linen: cotton has shorter strands and is very twisted looking, while linen is smoother
-wool vs. silk: wool has a very rough surface, and looks like hair, which has lots of ridges, while silk is smooth
-nylon vs. polyester: after looking all over the internet, I still can’t figure this one out
-practice doing them on your own to figure out what they are (especially nylon and polyester); do burn tests and look at them under a microscope
-Regional:
-swatches of the actual fabrics were provided (a towel, a linen tablecloth, and corduroy)
-don’t have to use burn test or microscope
-just know what each fabric is used for
-States:
-consistently for two years, State has provided eight fibers, two per suspect
-know how do identify fibers under a microscope
-there are eight microscopes up at the front of the room, each with a sample of the fiber already on a slide and ready to go
-know how to perform a burn test
-each team is given a little cotton-ball-sized ball of fiber which then can use for burn test
-Nationals:
-know how to do a burn test on only one strand of fiber
-don’t use more than one strand, which is more difficult than a ball
-be prepared to make an identification using a microscope making your own wet mount (this will NOT already be done for you)
d) Hairs
-General:
-the best way to identify is using a microscope
-however, if possible, be familiar with the texture and feel of a pile of dog hair, a pile of cat hair, and a pile of human hair
-Regional:
-hair samples were provided to look at through a plastic baggy, but not to look at under a microscope
-just know general texture I guess, there’s not much else to do
-State:
-I’ve never had to do this at State, so I can’t say for sure
-I would guess you should know how to distinguish between a human, cat, and dog hair under a microscope
-still be familiar with the feel
-Nationals:
-each team can have only one strand of hair per suspect
-make identification under microscope using your own wet mount (which will NOT already be done for you)
-at this point, it’s less useful to be able to do this by touch, since there’s only one hair given
e) Chromatography
-General:
-know how to find the Rf value (rate of flow)
-if they ask for the Rf value, measure from the middle of the splotch
-if they ask for the Rf value of the smallest particle, measure from the top of the splotch, since those particles have traveled the farthest
-Regional:
-I’ve never done this at regional
-I would imagine the most you would need to do is interpret results that are given
-States:
-just be able to find the Rf value from results that are given
-given results are basically just a little diagram that looks like a strip with an ellipse on it with a starting line
-Nationals:
-be able to do your own paper chromatography
-know how to do paper as well as strip
-in Kansas, the woman yelled at everyone about how if we ripped their sheet of chromatography paper into strips, we would be disqualified
-also, in this case, be prepared to do up to eight chromatography tests all side by side (ours were 4 syrups and 4 inks from pens)
-doing your own chromatography is VERY different from reading off results, and by very different, I mean much harder; PRACTICE; here are two problems I ran into:
1) Make sure you have some way to suspend your chromatography in the water so you can move on to another part of the test; I was immobilized since I had to hold mine for five minutes with no way of propping it up
2) I’m not sure what you do if the water travels up to the top of your strip; you’re supposed to measure the particles of the substance travel over the distance that the water travels, but it’s possible that the water might have been able to travel longer if there had been more paper; talk to Ms. Koch about this one
f) Spectrography: I honestly don’t know anything about this one, since it’s the job of the chemistry person
g) Fingerprints
-Usually there are two parts to this:
1) Matching a picture of a fingerprint to another picture of a fingerprint; this is very easy
2) Describing the fingerprint, and what parts about the two match
-usually this is an opportunity for you to show what you know about fingerprints, and the more you specific details and terms you can put down, the better
-Three major things to know to categorize fingerprints
1) Categories: arch, whorl, loop
2) Sub-Categories:
-Arch: Plain Arch, Tented Arch
-Loop: Radial Loop, Ulnar Loop (this has never been relevant in any competitions I’ve done, since you need to know if it is on the right or left hand to make this ID, and that info usually isn’t specified)
-Whorl: Plain Whorl, Central Pocket Loop Whorl, Double Loop Whorl, Accidental Whorl)
3) Other Indicators: the most usual are ridge ending, bifurcation, island, core, bridge, and dot, but I have a list of others that might be asked for along with their pictures, which might be helpful
-Regional:
-At one competition, I was only asked to match the fingerprint pictures without any terms
-At another, I was asked to match them and describe why they were the same
-example: both are tented arches, both have two bifurcations
-Know the categories of fingerprints, and a few general “other indicators”; the sub-categories may be helpful
-States:
-One year they only offered pictures of the suspects’ fingerprints, and they verbally described the fingerprint found at the scene; this was more difficult than simply matching
-for this, know the categories, sub-categories, and some general “other indicators”
-Another year they offered pictures to match and asked the teams to describe what about them was similar (like the scenario described at regional)
-Nationals:
-Pictures of fingerprints of the suspects and crime scene are given, and they have to be matched
-3 questions about each print were asked:
1) Who does this print implicate?
2) Another question about the print
-examples: What type of print is this? Or, what is this print’s ridge count?
3) Pointing out something on the print
-examples: Circle the core on the given print and the print it matches. Or, circle an example of bifurcation on the given print and the print it matches.
-ALSO, random questions about how fingerprints are actually identified in real situations are asked
-know about AFIS (Automated Fingerprint Identification System), and how many matching points are needed for a positive ID
-know a little bit about how fingerprints are formed (basal cells while a fetus) and the layers of skin
-know how much of the population has each category of fingerprint
-know how different types of prints are lifted in different scenarios, and which chemicals are used to process them
-example: What method would you use to get a fingerprint off of a doorknob [or piece of paper, or refrigerator]? What chemical is used in this process?
h) DNA Chromatograms:
-General:
-I’ve never actually had to do one of these with a graph during a competition, but I think you just use the color key to order the DNA
-However, at nationals, they did give us a strand of a DNA sequence with just letters, and we had to match the strands to that of the victim
i) Glass Analysis:
-General: I’ve never had to do this in a competition, so I can’t tell you much
-if they ask at Regional or States, you probably just need to be able to figure out which blow to the glass came first, if there are multiple cracks; just remember that one crack won’t cross over a preceding crack
-at Nationals, they would probably expect you to know the Index of Refraction of certain types of glass and materials; I looked online for an hour or so and couldn’t figure this out, but maybe you would have better luck
j) Entomology:
-General: I’ve never had to do this in a competition, so I’m not entirely sure about it
-it’s impossible to determine specifically how long it takes for different species of bugs to enter a body, since it depends on what climate and what condition the body is in
-however, I would suggest knowing the general succession (flies, then beetles, then mites, etc.) and why
-These are the cliffs notes for the order of succession:
1) Bacteria: Decomposition begins with anaerobic bacteria, which devour the body from the inside out; these can tolerate the acidic environment created by the decomposition of the muscles; the bacteria neutralize the acid
2) Flies: Flies can’t feed on the body when it is acidic, but they can after it has been neutralized by the bacteria; they make the body more alkaline
3) Beetles: can’t feed of the body due to the alkaline condition created by the flies, but can feed off of the fly larvae
4) Wasps: wasps lay eggs inside of fly larvae
5) More Flies: as the body dries from “semiliquid” state, some species of flies leave, while new species of flies that prefer drier conditions come in
6) More Beetles: most species of beetles devour the body when it is entirely dry, since it is a good pH for them and they have mouthparts that allow them to latch onto the body
k) Spatters:
-General: I’ve never had to do this at a competition
-know that if a drop is circular, it came from directly above, but the more and more oval-shaped it is, the closer the angle that it came from was to the floor
-the most important equation to know is the “angle of impact”, which describes the angle from the floor and can be found in the Forensics notebook; it is possible to figure out exactly where the spatter came from using the diagram when it is IN COLOR (in black and white, it’s useless), however the most important is just knowing how to find the angle of impact; Akhil Jariwala and Guatam Sanka are both the most capable people of explaining this concept (which Ms. Koch doesn’t even understand it), so if you really want to figure it out, talk to them
l) Seeds and Pollen:
-General: I’ve never had to do this at a competition
-from my experience, the most I think they would make you do is compare slides of pollen under a microscope, in which case, know how to make a wet mount
m) Tracks and Soil:
-General:
-This is usually REALLY easy and pretty self-explanatory
-Maybe know some really general terms for soil
-the four types of soil are sandy, silt, clay, and loam (a mix of the three)
-Regional:
-Soil: they gave us a bag of red clay and a bag of sand, then said that red clay was found with one suspect and sand was found with another, so it was basically matching
-Nationals:
-Tracks: also matching, although these can be a little bit more difficult, since the pictures aren’t as clear; usually there’s a picture of a footprint or a tire track, then a picture of bottom or a shoe and a print of a few different tracks
n) Analysis and Answers
-General:
-use the clues that you know to figure out the parts that you have more difficulty with or are unsure of
-Regional:
-this is usually really open-ended, with a blank sheet of paper at the end to write up all of your observations and conclusions
-usually, there is only one suspect who committed the crime (instead of two or more working together), so the clues should only lead to one person
-States:
-States is usually more fill-in-the-blank with the specific answers, and there is no space given to write out a paragraph-style analysis
-at the top of each page, you must circle whether the suspect committed the crime or not (by circling yes or no), so this is pretty straight-forward, with only one person committing the crime
-Nationals:
-from what I’ve seen, there are a lot of fill-in-the-blank answers, as well as a large amount of space for a written, paragraph-style analysis