Past Forensic Quizzes

5/16/06 How is angle of origin determined from bloodstains? Sin of angle = width /length 3/27/06 What is polarized light? Polarized light occurs when the light waves are vibrating in a single plane. To really explain this would take much more time and expertise than I have, but the forensic application is this: many substances have optical properties which can be detected using a polarized light microscope, such as synthetic fibers, pollens and tempered glass. 3/1/06 What are 'natural' fibers? "Natural" fibers come from plants or animals. Because they are not perfectly consistent, they don't lend themselves to chemical or polarized light analysis. Using a set of reference slides, an examiner can distinguish cotton from linen from wool, and then the color can be compared with a comparison microscope. Examiners who had the time and ability used to extract the dye used and analyze that with chromatography, but it was a very delicate process. Rayon is reconstituted cotton, and considered sort of a cross between a natural and synthetic fiber. 1/15/06 What is an "expert witness"? According to Douglas Danner's "Expert Witness Checklists": "An 'expert' is a witness who is permitted to testify as to matters about which the trier of fact has insufficient personal knowledge to make the inferences necessary to arrive at a decision on the ultimate issues in dispute. Similarly, 'expert testimony' is that class of matters as to which a person acquires knowledge only by means of some peculiar experience not shared by the population generally. " The 'trier of fact' is the jury, or the judge in a bench trial. The expert is 'permitted' to testify because otherwise they would have no right to, not being involved in the case as a witness or partipant. 1/2/06 What does the size of bloodspatter stains tell you? Generally speaking, the smaller and finer the blood drops are, the velocity of impact was higher. So a gunshot produces many drops of perhaps less than a millimeter, whereas a brick to the head will produce fewer and much larger drops. 12/19/05 A falling drop of blood forms what shape while in flight? A falling drop of blood forms a sphere while in flight. Hint: This applies to gunshot primer residue as well. ALL liquids form spheres in free motion. It's the geometric shape with the smallest surface area. Hah! I WAS paying attention in 11th grade physics! 12-5-05 What's an incised wound (as opposed to a stab wound)? An incised wound is a 'cutting' wound, where the flesh has been slashed rather than the knife stabbed in. 11/28/05 What is lividity? (And it's not being really, really mad.) Lividity refers to the pooling of the blood after death. Gravity will cause blood to collect at the lowest areas--the back surface if the body is lying on its back, the lower legs if it's somehow upright. As decomposition starts and the blood coagulates, lividity will become fixed. If lividity is not consistent with the position of the body when it is found, then the body may have been moved after death. 11/21/05 What are STRs? Short Tandem Repeats, or sequences of DNA base pairs that are repeated end to end--how many times they're repeated is what will vary from person to person. 11/14/05 What is the average lifespan of an adult housefly? 20-30 days. (This does not include the egg and larval stages, which take about ten additional days.) 10/25/05 What do you call a hurricane in Florida? Normal summer weather. Not that I'm bitter or anything. 10/17/05 What is the Henry system? The Henry system is a classification and filing system for the ten fingers of each hand, designed in 1897 by an Englishman, Sir Edward Richard Henry and an Indian, Khan Bahadur Azizul Haque. A typical Henry classification could read: 12 M 8 A-t 11 over I 17 U-a. Yikes. I am SO glad computers came along. 10/10/05 What is a mode of occlusion? Bite. As in the pattern your teeth make when you bite someone. Didn't your mother tell you that was nasty? 9/28/05 What is a contact wound? A contact wound is when the muzzle of the gun is pressed against the body. The expanding gases, along with the bullet, cause a cross-shaped tear in the clothing or flesh rather than a smooth, round hole. 8/22/05 What is ninhydrin? Ninhydrin is sprayed or soaked onto paper to turn latent prints purple. This process can work immediately or it can take several days. The ninhydrin will continue to process until the entire paper is purple unless stopped and frozen with a developer. Checks and notes are commonly developed with ninhydrin. 3/7/05: What are the three basic fingerprint patterns, and which is the least common? Loops (ridges enter one side and exit the same side); whorls (ridges form a swirl or roughly circular pattern in the finger); and arches (ridges enter one side and exit the other). The least common, though by no means rare, is the arch.

8/15/05 How are gastric contents analyzed to indicate time of death? Perhaps other labs have more sophisticated methods, but this is how we used to do it: First you put on at least two masks because it is going to smell like someone threw up. Then you shake the jar to homogenize the contents. Then you get your water running, pour part of the jar's contents into a small strainer, and rinse under running water to remove the fluids and acids from the solid food. Then you transfer the solids to a petri dish and put it under a stereomicroscope and poke the stuff around with picks, saying, "That looks like a piece of tomato. That looks like green pepper. What's this stuff? Chicken?" And that's how we used to do it. 3/14/05 What is luminol used for? A luminol mixture will cause blood to fluoresce (glow). Unlike TV, no special light or goggles are required, but the area needs to be DARK. Just turning out the lights is not enough. Pitch black is best. Also, the glow will immediately begin to fade, so you have to work quickly. The results can be photographed with special infrared film and lighting but it's a lot more complicated than point and click. 3/21/05 What is amylase? Amylase is a digestive enzyme, usually used in forensics to identify a stain as saliva as opposed to some other bodily fluid. 3/28/05 What's the difference between a deposition and a statement? A statement is a written testimony by a witness or some involved party. A deposition is given in front of the prosecuting and defense attorneys and they can ask questions. The entire proceeding is recorded by a court reporter but there is no judge or jury present. For a witness, it can be more comfortable than a trial for that reason, but on the other hand, the attorneys can ask whatever they like without fear of irritating the judge or alienating the jury. 4/4/05 What does a GRIM II measure? (And no, it's not the gross-out content of movies and TV shows!) A GRIM (Glass Refractive Index Measurement) measures the refractive index of glass, to help determine if two samples of glass might have come from the same source. If they have a different RI, then they could not have a common source. If they have the same RI, they might have a common source. The samples would then go on to ICP (Inductively Coupled Plasma Mass Spectrometry) for elemental analysis to determine if they are the same. 4/11/05 What's better to use at a crime scene, photographs or videotape? We could debate this for hours, but generally, still photographs (either digital or film) are given a higher priority than videotapes. If you can do both, great. If you can only do one, it's always photographs. 5/2/05 What two elements indicate the presence of gunshot residue? Barium and antimony indicate the presence of primer residue from a bullet. We say "indicate" because barium and antimony can be found in other substances as well--say, paint, or firecrackers. Lead, of course, also indicates firearm activity. Unfortunately for our general health, however, lead is so common in the environment that its presence is not necessarily significant. 5/9/05 What is phenophthalein? Phenophthalein is used to confirm that something that looks like blood really is blood. First you drop alcohol on your sample, then phenolphthalein, then hydrogen peroxide. A deep pink color indicates blood. Contrary to what you see on TV, you DROP the fluids onto the sample--never touch the bottle to your sample, unless you really want to contaminate your reagents and have to throw them out. 5/23/05 What is a "grow house"? A "grow house" appears, from the outside, to be a normal, mild-mannered suburban home. Inside, the rooms have been equipped with an irrigation system, high-intensity lights, reflective wall coverings, air conditioners and fans, cultivating marijuana plants to grow nearly to the ceiling. These houses use a prodigious amount of electricity, and smell. Bad. 6/6/05 What is a buccal swab? A swab of buccal cells (the cells that line the inside of your cheeks--the cheeks on your face, I mean) usually used for DNA testing. Staff often use this term interchangeably with 'a saliva sample' -- not the same thing but usually serve to get the same result. Much easier (and less painful!) than drawing blood. 6/20/05 If you have a pane of glass with more than one bullet hole in it, can you tell which shot came first? Possibly. Cracks will end when they encounter previous cracks, so look at the concentric and radial cracks resulting from each individual hole. If the cracks from bullet hole A end in cracks from bullet hole B, then B came first. 7/2/05 How long do fingerprints last? It depends. (Hint: In real life, a great deal of forensic evidence and its significance "depends".) It depends mostly on environment. If the print is deposited somewhere steadily dry and a little cool, it can stay for years. Possibly centuries. If it's deposited where the temperature and humidity vary (or in a house in Florida in summer with no A/C, like the one I spent hours in this weekend...I think I sweated off ten pounds) it might not last hours. 7/11/05 Can you develop fingerprints left in blood? Bloody fingerprints, even very faint ones, can be stained with Amido Black to produce a nice, clear print. 7/18/05 No quiz this week! I'm on a cruise having fun! 7/25/05 What does ABC stand for in the field of forensics? The American Board of Criminalistics. 8/1/05 What is caliber, in relation to firearms? Caliber is usually the diameter of the barrel, measuring from the lands, not the grooves, expressed in hundreths of an inch--so a 45 caliber bullet should be 45/100 of an inch in diameter. 8-8-05 How are fibers analyzed? Synthetic fibers can be analyzed chemically to determine if they are nylon, polyester, etc. Both natural (cotton, linen) and synthetic fibers are examined with a light microscope for diameter, color, cross-sectional shape and appearance to determine if they are consistent with having a common origin. However, you can almost never say that this orange fiber came from this suspect's T-shirt, because you have no way to know how many of those T-shirts exist in the area.