Crime Busters

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In Crime Busters, students will identify perpetrators of a certain crime by identifying unknown powders, liquids, and metals, and analyzing hairs, fibers, plastics, fingerprints, DNA evidence, shoeprints, tire treads, soil and splatters. Students will also analyze evidence from paper chromatography. Students should be able to use this data to answer some questions about who committed the crime and how the evidence supports their argument. This event was previously known as Science Crime Busters, but was changed to Crime Busters after the 2009-2010 season.

Some elements of this event are similar to its Division C equivalent, Forensics. The information contained in that page may be used as enrichment for a competitor who has already learned the basics.


Every team must bring these safety items to be allowed to participate.

  • Lab aprons or lab coats. If a team uses lab aprons, they must make sure to wear long sleeves that reach the wrists.
  • Closed toe shoes, NO sandals
  • Pants or skirts that cover the legs to the ankles
  • Category C Goggles

Also, the team should and may have the following:

  • One 8.5"x11" page with information on the front and back
  • Writing instruments(pencils!)
  • Paper Towels
  • Magnets
  • Microscope slides and cover slips
  • Tweezers or forceps
  • pH paper
  • Hand lenses
  • Test tubes and racks, spot plates, well plates, reaction plates, beakers, or similar small containers for mixing
  • Something for scooping, stirring, and mixing
  • Pipettes or droppers
  • Graduated cylinders (10 mL and 25 mL)
  • Conductivity meter (9V or less)

The supervisor will provide everything else needed, so if anything outside of what the rules allow is brought, a penalty may be issued.

Before the competition (at school practices)

Check with your SO coach to get the following materials to test:

  • Powders
    • White Sand
    • Calcium Carbonate
    • Table Salt
    • Sugar
    • Flour
    • Cornstarch
    • Gypsum
    • Baking Soda
    • Powdered Gelatin
    • Alka-Seltzer(may not be powdered completely, as the event supervisors may have to crush it themselves)
    • Sodium Acetate
    • Vitamin C
    • Yeast
  • Metals
    • Aluminum
    • Copper
    • Iron
    • Tin
    • Zinc
    • Magnesium
  • Liquids
    • Rubbing Alcohol
    • Household Ammonia
    • Water
    • Vinegar
    • Hydrogen Peroxide
    • Lemon Juice

The coach will also need-

  • a dropper bottle of 1M HCl (hydrochloric acid)
  • a dropper bottle of Iodine
  • pH or Litmus paper
  • 15-20 unknowns
  • 250 mL distilled H2O
  • chromatography materials (chromatography paper, ink to be tested, extra beaker for testing)

Make a chart for testing. For powders, include color, reactions with water, HCl, and Iodine; odor (distinct, faint, or none); shape (crystalline, granular, or powder), solubility (whether it dissolves in water or not), and reaction to pH or Litmus paper. For metals, include reactions to HCl and magnetic property (yes or no). For liquids, include smell, reactions to pH or litmus, and color. With your teammate, memorize the results (this is where two heads are better than one) and try testing unknowns made by the coach or other team members. This helps very much when it comes time for the competition.



Powder Crystal Shape Color Solubility pH HCl Iodine Formula Notes Other Names
Sodium Acetate powder - irregular shape white yes ~8 none none NaC2H3O2 exothermic when mixed with water and has a distinctive sweet odor
Sand random white no ~6 none none; bad odor SiO2 does nothing, may have black specks
Calcium Carbonate powder white no ~7-8 fizz none; the color looks sort of like mustard/peanut butter CaCO3 the powder it self is very airy and hole-y Limestone, chalk, aragonite
Vitamin C grains white yes ~2 none clears it C6H8O6 may have a colored tint- green, yellow, pink, orange (if from tablets). Distinctive smell. Ascorbic Acid
Salt signature square grains white yes ~6-7 none none NaCl delayed reaction with iodine (may be difficult to observe) Table salt
Sugar grains white yes ~6-7 none none C12H22O11 Similar to salt but grains are slightly rounded Sucrose
Flour powder Off-white no; lumpy ~6-7 none blackens it - iodine clumps together, unlike cornstarch (C6H10O5)n Clumps with water
Cornstarch powder white no - forms solid-liquid substance ~6-7 none blackens it C27H48O20 pure white, feels slippery
Gelatin grains light yellow no; turns into gel over time ~6 none none C102H151O39N31 swells in water
Alka-Seltzer powder white yes ~6-7 fizz fizz C16H17NaO14 fizzes with everything including water
Yeast pellets tan no ~7 none none microorganism generally easy to identify since it smells sort of like bread most of the time Saccharomyces Cerevisiae
Baking Soda powder white yes ~8 extremely fizzy for a long while none; more red-brown than Plaster of Paris NaHCO3 rough texture (kinda) Sodium bicarbonate, sodium hydrogen carbonate
Gypsum powder white no ~6 none none CaSO4· 2H2O opaque bubbles and hardens in water Plaster of Paris, calcium sulfate dihydrate, alabaster

Many powders have a "give-away" making them easier to identify:

  • Alka-Seltzer fizzes with everything you mix it with
  • Yeast smells like bread and is the only tan powder
  • Gelatin swells in water and is the only one to do that
  • Ascorbic acid (Vitamin C) is the only acidic powder, and the only one that clears in Iodine
  • Salt has the only square grains

Keep in mind, pH is the negative log of H+ concentration, which means the more sample you add for the same amount of water, the further your pH will be from neutral (7). It is recommended that you make your own chart of test results and then check that against information found online, but this is especially important for pH.

Pay attention to what the powder looks like. If you practice a lot and learn to identify certain powders on sight, you don't need to run any tests on it and it will save a lot of time.


Liquid Color pH Scent Iodine Formula Notes Scientific Name
Lemon Juice Cloudy, yellowish ~2-3 citrus none C6H8O7 expect pulp Citric Acid
Rubbing Alcohol clear ~6 sweet, similar to alcohol none C3H8O slightly sweet smelling Isopropanol, Isopropyl Alcohol
Ammonia Cloudy, especially after shaking ~10-11 pungent none NH3 expect it to be some random color and scent Azane
Vinegar clear ~2-3 sour none CH3COOH very strong scent Acetic Acid
Water clear ~7 none none H2O nothing special about it Dihydrogen Monoxide
Hydrogen Peroxide clear ~6 none tiny delayed bubbles H2O2 delayed reaction in iodine, bubbles of oxygen appear when shaken

Each liquid has a "give-away", making them fairly easy to identify-

  • Lemon Juice has a strong lemon odor (and is a strong acid, like vinegar)
  • Ammonia is the only strong base
    • It is best to use pH paper first, before smelling the unknown liquid, so that you will never have to smell ammonia (even if by wafting) since it can be chosen conclusively if the unknown liquid has a very basic pH.
  • Vinegar has a distinctive vinegar odor (and is a strong acid, like lemon juice)
  • Rubbing Alcohol is neutral, but has a distinctive odor
  • Hydrogen Peroxide and water are very similar (both are odorless, neutral liquids), but there is a simple way to tell them apart. Fill a small well in your testing tray with the liquid, put in a few drops of iodine and stir. After about a minute (though sometimes more), tons of bubbles will appear if it is hydrogen peroxide, while nothing will happen in water (besides the color change due to iodine's color).


Metal Color Density Water HCl Magnetic Formula Atomic Number Notes
Aluminum gray light none little fizz no Al 13 delayed reaction with HCl, takes a long time, not reliable
Copper copper heavy none none no Cu 29 very easy to ID
Iron black heavy none fizz yes Fe 26 delayed reaction with HCl and smells bad, almost like rotten eggs
Tin gray light none little fizz, immediate no Sn 50 yellow tint
Zinc gray heavy none fizz, immediate no Zn 30 shiny
Magnesium gray light little fizz after a while fizzes and loses color; dissolves after a while no Mg 12 dull

Almost every metal has a "give-away", making them fairly easy to identify-

  • Iron is the only magnetic metal
  • Copper is the only metal with a color other than grey (or similar).
  • Magnesium will often steam with HCl, and will also let off a strong odor when HCl is added.
  • Zinc will react vigorously (but will not steam) with HCl, and is non-magnetic.
  • Tin and aluminum are very similar (neither react very much with HCl), but there are a few things that can be done to tell them apart. First, tin often has a yellowish tint, which aluminum will never have. Next, tin is often fairly shiny, while aluminum is dull. Lastly, if the metal is very malleable, it is probably aluminum (think aluminum foil).


In Crime Busters, there are 3 nonmetals which can never be mixed in the event: yeast, vitamin C, and sodium acetate. Everything left is neutral or basic and non-biological.

The key to finding the components to a mixture is to react each off individually. If there appears to be a powder and a crystalline component, add HCl or iodine to a sample. If the iodine turns blue, finding the first component will be straightforward because you will only need to find the pH of the mixture with water. A more neutral pH will mean that the noncrystalline component is flour; a more basic pH will mean cornstarch. If the iodine fizzes (and the HCl), then the component is Alka-Seltzer. A fizz with only the HCl means the component is either CaCO3 or NaHCO3. Once again, a pH test will show the difference: a neutral pH means calcium carbonate, and a basic pH means baking soda. No reaction means gypsum. To find the crystal, test for solubility. Sand will not dissolve, whereas salt and sugar will. The difference between the latter two is that salt has cubic crystals, and sugar has irregular crystals.

Two crystals are fairly easy to separate because the HCl and iodine can be skipped, and only solubility needs to be tested. Once again, a component that does not dissolve is sand, and a component that does is either salt or sugar, which can be differentiated by crystal shape. If both dissolve, the mixture is salt and sugar (probably the single most common mixture in this event).

For two powders, test with iodine first, then HCl if not all of the mixture fizzed or turned blue, and finally pH if needed. Go off of the information above to find each, and use logic if two things react at once.


This is very easy to do but must be done with care. Place a dot of ink (solute) at one end of a strip of filter paper. Then, get a small cup of solvent (often dH2O) and put the paper on the cup just so that the ink dot is above the waterline. Wait for the colors to separate, and that's it! Once the colors have stabilized, remove the paper from the solvent, and quickly put a line in pencil where the top edge of the water is on the paper. This allows you to find the Rf (retention factor or retardation factor) value of any ink spot if it is included in a question.

For practicing paper chromatography at home, use a coffee filter paper or paper towel if you do not have chromatography paper. Alcohol-soluble markers and pens will not work if using water, and if they do, the results won't be very visible. Using water-soluble markers/pens like Expo or Vis-a-Vis will get you the best results.

In paper chromatography, the paper is the stationary phase and the solvent is the mobile phase. The higher the Rf value, the higher the affinity the solute has for the mobile phase, and the lower the Rf value, the higher the affinity the solute has for the stationary phase. If you place the ink dot under the water line, the ink dot will just dissolve, meaning that chromatography will not be performed.

Participants may also be asked to measure the Rf value of a chromatogram. This is known simply as the ratio of the distance traveled by the solute to the distance traveled by the solvent. The Rf value is also dimensionless, meaning it has no specific unit of measurement.


Some of the basic fingerprint patterns

Practice identifying and comparing fingerprints. There are 3 basic categories of fingerprints(arches, loops, and whorls). They are easily identified by there general shape and number of deltas (triangles made from ridges). Make sure you know if your event supervisor is looking for the basic type (loop, arch, whorl), or the more in-depth name (Tented Arch, Ulnar Loop, etc.).

  • Arches= a hill shape with no deltas
    • Tented arch= an arch with a sharp corner at the top point
    • Plain arch= an arch with a more rounded top point
  • Loops= a beanish shape with one delta
    • Ulnar Loop= A loop pointing towards the pinky
    • Radial Loop= A loop pointing towards the thumb
  • Whorls= a circle-like shape with two or more deltas
    • There are many sub-categories of whorls, such as (but not limited to)-
      • Plain whorls
      • Central Pocket
      • Double loops
      • Accidental whorls


The polymers required for this event are PETE (1), HDPE (2), PVC (3), LDPE (4), PP (5), PS (6), and PMMA (7). HDPE, LDPE, and PP float in water while PETE-, PVC, PS, and PMMA do not. This means that the first group has a density of less than one and the second group more than one.

Identifying the polymers in the first group is easy. HDPE and LDPE are translucent while PP is not. HDPE is relatively more translucent then LDPE. Identifying in the second group is also fairly simple. PS will SLOWLY drop down in water or half of the flecks will sink while the other will float. PVC is sometimes rubbery, but never transparent, while PETE and PMMA are always clear. It is also good to have a chart on your cheat sheet with info about each of the plastics, which makes it easier to identify

Fiber Analysis

Natural fibers come from plants (cotton) or animals (wool). Manufactured fibers are synthetics like rayon, acetate, and polyester, which are made from long chains of molecules called polymers. To determine the shape and color of fibers from any of these fabrics, a microscopic examination is made.

Generally, the analysts get only a limited number of fibers to work with--sometimes only one. Whatever has been gathered from the crime scene is then compared against fibers from a suspect source, such as a car or home, and the fibers are laid side by side for visual inspection through a microscope.

The first step in fiber analysis is to compare color and diameter. If there is an agreement, then the analysis can go into another phase. Dyes can also be further analyzed with chromatography, which uses solvents to separate the dye's chemical constituents. Under a microscope, the analysts look for lengthwise striations or pits on a fiber's surface or unusual shapes.

When using a microscope to distinguish between animal, vegetable, and synthetic fibers, it can be difficult because there can be a seeming variety within a single fiber type, making it hard to tell what type it is. Generally variety within fiber types such as animal fibers is often because the magnification of the microscopes used to take the images of the fibers you find from searching on the internet is different. As an example, you may not be able to see the scales on a wool fiber under a microscope if the magnification isn't high enough. However, natural fibers usually have imperfections in width under a microscope. On the contrary, synthetic fibers usually are the same in width since they are man-made. After this, distinguishing between vegetable and animal fibers is usually just a matter of pattern difference.

In short, the fiber analysts compare the shape, dye content, size, chemical composition, and microscopic appearances, yet all of this is still about "class evidence". Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source, and there is no fiber database that provides a probability of origin.

Plant fibers are made from cellulose and/or other carbohydrates, animal fibers are made from keratin and/or other proteins, and synthetic fibers are made from hydrocarbons, such as petroleum, a mixture of hydrocarbons.

Here is a useful table that can help to identify common fibers used in competitions based on a burn test.

Animal Fibers
Fiber Smell Flame Withdrawn
Wool Burning Hair Small flickering flame, brittle ash, no smoldering Self-extinguishing
Silk Burning Feathers Calm, no smoldering, black beads, crushable Self-extinguishing
Vegetable Fibers
Fiber Smell Flame Withdrawn
Cotton Burning Paper Flame amber or yellow, slow burning, fluffy, greyish ash Continues to burn
Linen Burning grass Flame yellow, burns constantly, sparks Continues to burn, burns completely
Synthetic Fibers
Fiber Smell Flame Withdrawn
Nylon celery Orange, hard bead produced Self-extinguishing
Acrylic pungent Burn quickly, hard black bead that can be partially crushed Continues to melt
Polyester sweet/chemical Burns quickly, hard cream or black colored bead that cannot be rushed Continues to burn
Rayon Burning Wood Rapid burning flame, slow burning embers, no ash Continues to burn

Hair Analysis

Competitors are asked to know the difference between human, cat, and dog hair for competition. Microscopes are most commonly used for this, so studying images of different hairs is good practice for this portion of the event. Below are some examples of the required hair - overall, it is relatively easy to tell them apart. Cat hair has a scaly outside (cuticle) similar to human hair, though the core (medulla) is more broken or even invisible in human hair. Conversely, dog hair has a very thick medulla.

Microscopic Images of Hairs
Type of Hair Cat Dog Human
Image (s) Cat hair 1.jpgCathair2.jpg Dog hair 1.jpg Human hair 1.jpg

Along with identifying the difference between human, cat, and dog hair, competitors may also be asked general questions about hair. These may include but are not limited to phases of hair growth, information about the layers of the hair shaft, identifying the type of medulla or scale pattern of a hair strand under a microscope, and more. One common question that may be asked is the three layers of the hair shaft, which are cuticle, cortex, and medulla. (outside to inside)

Bloodstain Analysis

Competitors may be asked to identify the velocity of a single blood spatter, or multiple. It also may be asked to find the direction of the impact of a blood drop, which comes from the direction of the tail of the drop. If the blood drops of a spatter are smaller in diameter, the velocity of the spatter is larger. A good practice for this is to ask students for the velocity of various images of blood spatters. Some examples are shown below.

Blood Spatters
Velocity Image Diameter of Drops Speed Common Causes
Low 200px‎ 4 mm or more ≤ 5 feet/second Nosebleeds, small cuts, etc.
Medium Blood spatter med.gif 2-4 mm 5-100 feet/second Backstabbings, beatings, etc.
High Blood spatter high.gif < 2 mm > 100 feet/second Gunshots, bombings, etc.

Usually a murder from a crime scene would not occur because of a low-velocity spatter found at the site of the event. Medium-velocity spatters and high-velocity spatters, however unlike low-velocity spatters, are commonly found at an assassination where a bloodstain is found.


This section will be mostly be discussing more topics on general questions normally not related to the crime scene since a DNA section related to the crime scene on a test usually only has competitors match DNA (electropherograms, gel electrophoresis, PCR, et cetera) samples of one of the suspects to those found at the crime scene, which is quite simple by analyzing the images of each one.

DNA stands for deoxyribonucleic acid and makes up genes in the nucleus of cells. Humans have 23 gene pairs, 46 genes in total, half from each parent. These genes are found in living cells like your lung cells as an example but usually are not found in dead cells such as fingernails and hair besides the ones in your hair roots. Body fluids such as blood and saliva that contain cells also contain DNA. It is a nucleic acid, one of the four major types of macromolecules, and is shaped like a double-helix. Two biopolymers called polynucleotides make up this polymer, which comprises nucleotides. These nucleotides each have a nucleobase and a 2-deoxyribose sugar group linked to a phosphate group, forming a phosphate-deoxyribose backbone. The nucleobase can be either adenine, guanine, thymine, or cytosine, where adenine and guanine are the purines and the thymine and cytosine are the pyrimidines. Adenine pairs with thymine and guanine pairs with cytosine, where they bind through covalent (also referred to as hydrogen) bonds.


Soil is usually included on a test as an identification lab test for one or more soil samples, but general questions may also be asked about soil. The six main types of soil are peaty, loamy, sandy, clay, chalky, and silty. A method to identify soil types is identifying them by the color of the soil. A dark brown color signifies a loamy soil, a darker brown color (almost black) signifies a peaty soil, sandy soil has a color of that of sand but darkened quite a bit. Clay soil has a slightly lighter color than sandy soil, chalky soil has a color similar to that of limestone, and silty soil has a similar color to loamy soil, but a slightly lighter color.

The pH of a soil sample may also be asked on a test using a powder and a labeled container you can put the soil sample in that tells you the pH of the soil based on color code. The following values of pH of each soil type may not be fully accurate, so it is recommended that you don't use them on your note sheets and check first to see if you get a different result when pH testing. Sandy soil has a pH of about 4.5-5.5, silty soil also has a pH of about 4.5-5.5, clay soil ph of about 5.5-7.0, loamy soil has a pH of about 5.5-6.5, peaty soil has a pH of about 3.0-4.0, chalky soil has a pH of about 7.1 or above. The ideal pH of plant growth is about 6 to about 8.

Some of the following may be asked on a test.

  • The diameter of silty, sandy, and clay soil from least to greatest is in the following order: clay, silty, and sandy.
  • Loamy soil is a mixture of sandy, silty, and clay soil and contains lots of organic matter, making it nutrient-rich and good for plant growth.
  • Peaty soil is acidic and very high in nutrients, but this can lead to the soil having fewer nutrients ultimately.

Shoeprints and Tire Tracks

These two topics are mostly matching using images of shoeprints and tire tracks, similar to some of the other topics in this event, however, the type of print may be asked. There are three types of prints: patent (also called visible), plastic, and latent. A patent print is one that is already visible to the human eye, such as a print from water or blood on the ground. Like a patent print, plastic prints are also visible when made, except that an imprint is made in the ground itself, a force is exerted on the ground by the shoe that causes the ground beneath the shoe to decrease a little in elevation, usually on a surface as mud or clay with high moisture, whereas patent prints just contact between the ground and the shoe, forming a print mark resembling the shoe from a substance that is visible. Latent prints are not visible and therefore need different kinds of methods depending on the print to uncover them so that they are visible. These methods are more explained in-depth at the Forensics page, where you can find a few examples.

Water Testing

Water Testing (no longer in the rules after 2010)
The rules describing water testing are very vague. They only specify what can be tested for, but not how they can be tested. Titrations, probes, and colored strips are some possible methods used. Below is a table of the very basics on each of the aspects included in water testing.
Measurement Units Low Mid-range High Description
Temperature #° Celcius Below 20° C 20-25° C (Room temp) Above 25° C Measure of heat
pH pH units 0-6.9 (Acid) ~7 (Neutral) 7.1-14 (Base) Measure of acidity/alkalinity
Hardness Parts per million (ppm) 0-140 ppm (soft water) 140-320 ppm (slightly to moderately hard water) More than 320 (very hard water) Measure of the amount of Sodium and Magnesium ions
Dissolved Oxygen (DO) Parts per million (ppm) 0-5 ppm (dangerous for fish) 6-8 ppm (habitable conditions) Above 9 (Very good for fish to flourish) Measure of the amount of gaseous oxygen (O2) dissolved
Biochemical/Biological Oxygen Demand (BOD) Milligrams per liter (mg/L) 1 mg/L (Pristine river) 2-8 mg/L (Moderately polluted river) 20;200 mg/L (Treated;Untreated Sewage) Measure of the quantity of the dissolved oxygen used by bacteria as they break down organic wastes
Chemical Oxygen Demand (COD) ? ? ? ? Measure of the capacity of water to consume oxygen during the decomposition of organic matter and the oxidation of inorganic chemicals
Turbidity Nephelometric Turbidity Unit (NTU) Less than 1 NTU (Ideal Drinking water) 1-5 NTU (Potable water) Above 5 NTU (Non-potable water) Measure of the degree to which the water loses its transparency due to the presence of suspended particulates
Common Cations Depends on test Depends on test Depends on test Depends on test "Common Cations" is a broad range of things with atoms that have lost an electron to become positively charged
Common Anions Depends on test Depends on test Depends on test Depends on test "Common Anions" is a broad range of things with atoms that have gained an electron to become negatively charged
Conductivity/Total Dissolved Solids (TDS) Parts per million (ppm) 0-140 ppm (Ideal drinking water) 140-400 ppm (Average tap water) Above 500 (Non-potable water) Measure of the ability of water to pass a current

Examples of Water Testing on Past Tests

2010 Southeast Pennsylvania Regionals- A few strips were given, very similar to pH paper, to be dipped into the water sample and compared to a chart that was provided by the supervisor. Teams then had to match the data (the crime scene liquid) to data provided for the liquids that the suspects were carrying (their water bottles) and say which it came from. There were 4 strips (so 4 tests total),similar to these. An estimated amount of time would be about five minutes.
2010 Pennsylvania States- Four liquids were given at a shared station, and teams had to do two tests on each: pH and some sort of titration (so 8 tests total). For the titration, a judge was there to explain how to do it, and written instructions were provided. Teams were intended to fill a container with the liquid, then added a certain number of drops of an indicator and a certain number of drops of another chemical, mixing continuously. Teams then had a tiny syringe filled with another chemical and slowly added it, mixing constantly until the solution turned purple (it was pink beforehand). This process could take anywhere between 10-20 minutes to complete, depending on how much practice teams had previously had with titrations.
2010 Nationals- Teams got four probes (conductivity, DO, pH, and temperature) and a TI graphing calculator (already set up to receive and display information from any probe when plugged in. No preparation was needed to understand how it worked since the judges gave written and verbal instructions). Teams then had an observation/conclusion sheet to record information. Teams wrote down the probe used and the numerical value received (0.5 points for each one of these pairs) and then had a line to write a conclusion based on the information (0.5 points for each of these). To get full credit (5 points), teams needed 5 data entries and 5 conclusions based on those entries. On the crime part of the test, they said "Liquid S (the one that teams tested) was found around the area of a freezer, dishwasher, and sink. Do the necessary tests to figure out exactly where it came from". This test didn't ask any supplemental questions about water testing, as it did for the powders, liquids, fingerprinting, DNA, etc.


Keep in mind that this portion of the event is worth 25% of the score. So, it is very important to leave enough time to get it done right!

An event supervisor will likely give few instructions besides something along the lines of: "Based on your analysis of the evidence, who is likely the culprit?" However, there are many things that they may be looking for beyond just a name-

Rationale based on physical evidence- Use the evidence to support your claim. Talk about every piece of physical evidence that points to that person. To connect someone to the crime scene, one could cite a connection like "Joe works with flour daily, and flour was found at the crime scene" or even more simply "Joe's fingerprints were found at the crime scene".
Reasons why it wasn't the other suspects- Even if the test does not explicitly ask for this, it is an excellent idea to include it in the essay. Write at least a sentence for each person (more than a sentence if there is a lot evidence pointing towards them and you have to explain more in-depth why it wasn't them). If there is a lot of evidence against a second person, but you're sure it wasn't them, then talk about a logical reason why there would be all of that evidence (for instance, "they work at the crime scene" is a common reason). Also, even if someone has no evidence against them, include that in the essay: "Joe had no evidence connecting him to the crime scene, so he was not the culprit".
Motives- Give a motive for the person suspected to be the culprit, or if the proctor gave possible motives in the bios, restate them. This can add a lot to the essay, and help support your claim even if the wrong person has been selected.
Multiple or No Culprits from List of Suspects- While most tests will have one culprit from the list of suspects, do not get trapped into thinking that it must be only one person. Some proctors may set up the test to point to two people working together, or they may leave insufficient evidence to point to anyone. If either is the case, adjust the essay structure to fit the claim, and make a logical explanation. If correct, you will likely do very well. If incorrect, a logical explanation should receive a decent amount of credit for the essay anyway to still allow for a high placing.
Essay Structure-This can never hurt to have and takes very little time to do. Having a planned structure can also save time when planning the essay during the event. A simple, yet effective structure goes as follows.
Intro Sentence- i.e. "Based on the evidence gathered, we concluded that the culprit was Joe".
Lead-in to evidence- i.e. "There is much evidence to support our conclusion"
State evidence in multiple sentences- i.e. "Flour was found at the crime scene, and Joe works with flour daily. Also, Joe's fingerprints and DNA were found at the crime scene. Finally, Joe.... etc."
Lead-in to other suspects- i.e. "In addition, Bob was the next likely suspect" *remember to put the suspects from most likely to least likely, as it is the easiest for the proctors to read
Sentence on each suspect- See "Reasons why it wasn't the other suspects" section above
Conclusion Sentence- i.e. "Therefore, it can be concluded that Joe was the culprit."

Multiple Short Essays

With the time crunch often imposed on the scorers, a sequence of shorter essays (50 words or less) may sometimes be asked as the analysis. These typically address specific areas of the analysis: something about the crime, how it was committed, who committed it, the sequence of events, or something else of that sort. However, this is quite rare, and you will often see the traditional format of analysis instead.

At the Competition

Once materials are given to teams and the supervisor starts the competition, start by doing the paper chromatography test. Then, look at the rest of the test and estimate how long it will take or how much there is to do. If it is a lot, make sure to split up the work in order to avoid having wasted potential and then not finish. While the chromatography is going, identify all the unknowns using the tests described above. Please note that at higher levels of the tournament (state, national) and even sometimes Regionals, different compounds may be combined with each other- for example, flour and Alka-Seltzer. While one person is testing unknowns, the other might want to do the fiber, hair, or polymer testing. If there is a microscope set up for the hairs, make sure to go there first, because it will get crowded near the end, when teams may have to waste time waiting. After all the unknowns are identified, read through the packet to learn about the crime scene, and answer the questions. Then, after questions have been answered, write out the crime solution essay, discussing how the team chose the culprit(s), based on their motive and supporting evidence (the unknowns the person was carrying compared to the substances found at the crime scene). Following the supervisor's instructions, hand in the test and answers, clean up your lab area and relax until the supervisor dismisses the teams.

Make sure to leave enough time for the essay. Depending on the crime, it may be simple or extremely complex

WARNING: The rules say teams will get 50 minutes. However, the 50 includes the supervisor talking about safety/tips/rules/etc, so often teams will only have 40-45 minutes to actually work. It is probably a good idea to practice with only 40-45 minutes to get used to competition conditions. At 2010 Nationals, a brief introduction was given, then 45 minutes to work, along with a 5 or 10 minute clean-up time after teams handed in their tests.

HINT: In some competitions, teams may not get full points for ONLY identifying the substance. In many instances, teams will be given a blank chart that must be filled in with observations. These observations may include (but are not limited to): HCl test reactions, Iodine test reactions, pH, Solubility in water, Shape, Size, or Color. Even though with one simple HCl and water test, one could figure out Alka-Seltzer, taking time to test it or write down all observations could help. Even if you skip a small portion, such as hairs, placing is still possible if all observations were written down, and not just the identity of the substance, seeing as the identification and process of identifying the substance is worth 50% of the points. Some supervisors will even put a scoring chart on the front/back of the handout/packet to show the breakdown of points. Even if you fail to correctly identify a substance, the supervisor could award partial credit for filling in observations.


The scoring is composed of these elements:

  • Unknowns Identification (50% of total score) (Second Tiebreaker)
  • Chromatography (5%)
  • Polymer Testing/Natural and Man-Made Substances (Replaced Water Testing) (10%) (Third Tiebreaker)
  • DNA, fingerprinting, tire treads, fingerprints, shoe prints (10%)
  • Crime Solution Essay (25%) (First Tiebreaker)

Note: many tests do not follow this format

Practice Tests

  • Note: You will need to print off the fingerprints, shoeprints, and DNA yourself for the following tests.
"Dwisney Stars-Twenty Years Later" Test
"Dwisney Stars-Twenty Years Later" Answer Key
2009 Northridge Invitational Test
2009 Northridge Invitational Answers
Smorgan6's Practice worksheet
Smorgan6's Practice worksheet Key