Joined: 22 December 2005
it might just sound funny but let me tell u dat after watching ss iam really getting interested in forensic sciences.so much so dat i made my college project on d same topic.
while searching for d info i came across some interesting topics on fingerprinting and stuff . if u guys are interested i can upload it for u people.
but there is a problem ,i dont really know how to upload d stuff here.(i m bad at all these things u see)
so if any cud just tell me how to go abt it. it will be of great help.
Joined: 02 February 2006
Joined: 20 October 2005
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Joined: 22 December 2005
Fingerprints. There are three basic fingerprint patterns: Loops, Arches and Whorls. Everyone falls into one of these three patterns (diagram). Within these patterns are what we call minutia points. There are about thirty different types of minutae points, and no two people have the same types of minutae in the same number in the same places on their fingertips. This is why our fingerprints are totally unique.
Your fingerprint patterns are hereditary. They are formed before you are born, while you are still in the womb, they never change through out your lifetime, and they are even around for awhile after you die. So, why are fingerprints so good for identification purposes? They are totally unique, and they never change. Your fingerprints are formed underneath your skin in a layer called dermal papilae. As long as that layer of papilae is there, your fingerprints will always come back, even after scarring or burning. Gloves don't necessarily help you from leaving fingerprints. Surgical gloves were made to keep surgeons from infecting their patients. You can actually leave prints through surgical gloves. Surgical gloves were made to keep sterile conditions during operations. They have to fit like a second skin for surgeons to be able to pick up their instruments. They fit so tightly that fingerprints 'pass through' the latex membrane. They can also be turned inside out to yield fingerprints from the inside surfaces. Leather gloves can be treated in the same manner. Also, leather gloves can leave a print that is unique to that glove and no other (leather comes from cow skin, which is just as random as human skin). Even cloth gloves, such as mittens, can leave a distinctive print that can be traced back to the mitten that made it. Prints are left on a surface because we are constantly secreting water and body oils and other compounds through our pores. This material is left on the surface we touch in the form of a fingerprint. Different surfaces require different techniques for developing prints. In the movies, you usually see detectives with brushes. They are powder processing the prints. Minute particles of powder cling to the print residue as the brush passes over it. The print is then lifted with tape. Another process involves fuming. Vapors of iodine and superglue (bonds in seconds) will coalesce inside the print residue to reveal a latent print. Try this at home: You will need a zip lock baggie, a tube of superglue (i've found the gel version works a little better) and a can of soda or drinking glass. Place the can or glass in the zip lock baggie. Lay the baggie flat on the counter. Squeeze out a generous amount of superglue into the baggie (don't glue the glass to the baggie). Seal up the baggie. If you can, blow some hot, moist air into the baggie, like when you're trying to fog up a window with your breath. Seal it tight. The vapors from the superglue will build up in the tiny zip lock atmosphere and creep up into the prints on the glass or can. There, they will crystallize and, after awhile, you should see starchy white fingerprints develop on the glass or can. There are special processes that develop prints on paper, wood and cardboard. Fingerprints can be developed on objects that have been in water. Prints can be developed off of skin (such as from the neck of a strangulation victim). There are very few surfaces on which a print cannot be developed. Computers have revolutionized the techniques used to match fingerprints. Until recently, the old standard was the Henry Classification System; a cumbersome sequence of letters and numbers broken down into several levels of classification. It could take weeks, sometimes months to compare a suspect fingerprint to a department's print files. The advent of digital technology has changed all of that. Prints can be image scanned directly into a computer, doing away with ink and fingerprint cards. Prints can be compared at a rate of 400,000 per second. You couldn't do that in your lifetime. It's called AFIS. Automated Fingerprint Identification System. Departments will input all the prints from arrests and all of the print cards they already have on file to create an historical record. They also input all of the prints from any unsolved crimes, in the hope that a hit might come up from a routine arrest. Local departments are linking their systems into a national database. The FBI wants national standards and a fully functional national network in place by the year 2000. With a national network, you could get busted in New York and have a print hit come up from a crime you committed in California.
DNA. A quick primer on DNA: DNA is constructed like a ladder; a ladder that has been grabbed at both ends and twisted, creating the double helix shape. The rails of the ladder are phosphate and sugar groups. They link together (sugar+phosphate+sugar+phosphate) to form the backbone. So far it's not so tough. There are four bases that form the rungs of the ladder: Cytocene, Guanine, Thiamine and Adnine. They are always in pairs and always complement each other; Cytocene is always paired with Guanine and Thiamine is always paired with Adnine. Each base forms half of the rung, meeting in the middle. Now, think of that ladder as a zipper. When DNA replicates, is unzips down the middle, separating the base pairs like a zipper. The complementary bases now attach to the opened segments to make new DNA. One DNA analysis technique looks at junk DNA. Everybodys' DNA is pretty similar. Everyone who has blue eyes has pretty much the same code for blue eyes. Everyone who has brown hair has pretty much the same code for brown hair. But these coding sequences are separated by 'junk' DNA. This 'junk' DNA is non-coding and only serves to separate the coding sequences. These 'junk' DNA sequences are totally random and totally unique to an individual. The process is extremely technical, but that is the concept, and it's really not that hard to understand. Now, the way this works in a criminal case is thusly: The examining labs have samples of DNA, taken from a representative population group. These are entered into a database, to which the questioned DNA (that being compared for analysis in a case) is compared for frequency among the population group. That is DNA testing at its most basic. Other Sub-disciplines. There are numerous other areas of study in the field of personal identification. Forensic Anthropology seeks to identify remains, such as bones. From a skeleton, you can tell if the subject is human, its sex, the age of the subject when death occurred, stature, how long the remains have been in their current state and the cause of death. Facial Reconstruction gets in the media once in awhile. The photo imposition technique involves imposing a photo of the skull over a photo of the face in question. This is examined in the Romanov book in the 'suggested reading' link. Three dimensional reconstruction technique involves adding depth markers for tissue thickness onto a skull. The depths are an average taken from cadavers. Clay is placed over the skull, to match the depth of the markers, to simulate skin and muscle. The features are then smoothed out to make a 'face.' This has worked in a number of missing persons cases, but is considered more art than science. Hair Comparisons are another biggie in forensic science. Hair can be determined to be human or animal. The body area from which a questioned hair came can be identified. Race can sometimes be determined. Disease conditions can be determined. And, of course, a hair found at a crime scene can be matched to the person that left it there. It's a relatively simple comparison, involving side by side examination of the suspect and known hairs, similar to bullet matching.
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Joined: 22 December 2005
Firearms and toolmark identification involves more than just guns. Also included in this broad subject area are explosives, imprint evidence and toolmark evidence. Most physical evidence concerns itself with class characteristics and individual characteristics. Class characteristics are those characteristics which are common to a group of similar objects. For example, you buy a pair of Air Jordan sneakers. All Air Jordan sneakers have to same shape and same tread design on the bottom. These are class characteristics. Individual characteristics are those characteristics which are unique to a given object and set it apart from similar objects. You wear your Air Jordans around for awhile and they get worn. The treads wear down. They get little pits and gouges in them. These little pits and gouges are individual to your shoes and no others since no one has walked over the exact same surfaces in the exact same way in their Air Jordans. These two concepts, class and individual characteristics are the most important in firearms examination. A typical firearms examination concerns matching a bullet back to the gun that fired it, to the exclusion of all others. How can this be done? Bullet Matching. Certain parts of a firearm mark the bullet and cartridge. Rifling gives the bullet a signature marking that is unique to the weapon that fired it. Rifling exists as part of the manufacturing process of the firearm and serves to put spin on the bullet, giving it a straighter trajectory (much the same way a quarterback puts spin on a football). Rifling consists of lands and groves that spiral down the gun barrel (think of the seam on a paper towel tube). When the gunpowder in the cartridge is ignited, it forces the bullet down the gun barrel, expanding the soft lead into the lands and groves. As the bullet passes down the barrel, microscopic scratches from the lands and grooves mark the bullet. These microscopic scratches are a by-product of the manufacturing process and are totally unique to a particular firearm. Thus, the scratch marks on the bullet match the scratch marks in the barrel of the gun that fired it, to the exclusion of all other weapons. This is tested in the lab by test firing a bullet through the suspect weapon. The test fired bullet is then compared under a comparison microscope, side by side, to the bullet recovered from the crime scene. Both bullets are rotated until the striations can be made to line up, showing a match. If the striations cannot be lined up, the result is negative. Imprint Evidence. There are two basic types of imprint evidence: Three dimensional impressions, in which an object presses into something soft which retains the impression of that object; and two dimensional impressions, in which an object transfers an image to a surface or an object comes into contact with a surface that is coated and removes some of that coating. An example of a 3d impression is something stepping into mud. You've all seen Big Foot documentaries where a camper finds a huge foot print out in the woods. This is a 3d print. Big Foot (for lack of a better explanation) has stepped in the mud and left a foot print behind. The mud hardens as it dries and retains the print. An example of the first type of 2d print would be the step after you've stepped into spilled paint. The paint coats the bottom of your shoe when you step in it. It is then transferred to another surface when you step down. It is just like using a rubber ink stamp. An example of the second type of 2d imprint is when you stepped into the paint. You removed some of the paint, creating a negative image of the bottom of your shoe in the paint spill. Impression evidence can be so detailed, to the microscopic level, that it can be used to identify both class and individual characteristics. Not just used for shoes, impression evidence can also be used with tire impressions (a tire impression is just like a long, continuous shoe impression) and toolmarks. Tire impressions can be extremely useful. Let's say there is a bank robbery. The perpetrators parked behind the bank (as per the diagram below). As the fled, they unknowingly left behind a bunch of clues. Wheel base is the distance between the two front wheels and the distance between the front and rear wheels. There are guys in labs who have charted out these distances and can use this chart to narrow down the make of the car. The tread design itself, as discussed above, can narrow down the list of possible cars. There are books that contain images of every type of tire imprint, just for this purpose. The individual wear developed from use will show up in the impression, allowing for identification of a single car, to the exclusion of all others. We can also tell which way the car was facing, how they pulled out and in what direction. Toolmark Evidence. There are three types of toolmark impressions: Compression, in which a tool surface presses into a softer material; Sliding, in which a tool (such as a screwdriver, below) scrapes across a surface causing parallel striations; and cutting, which is a combination of the above two types (as with scissors). All three types can yield class and individual characteristics. In this way, marks left on a doorway from a pry bar can be matched back to that specific pry bar. Explosives. Without getting too into it, explosives residue can be analyzed to determine the type of explosive used in a particular detonation. Also, some manufacturers are now putting chemical tags in their explosives that will allow for tracking of specific batches by chemical composition or other tagants.
Joined: 22 December 2005
I'm not going to go into the basics of photography here. There are other pages on the web that will do it much better than I can. Actually, this section is going to be pretty short. There are just a few particulars to hit on, and a couple of interesting techniques. The first thing that needs to be done after securing the crime scene is photographing it. This creates a permanent record of the condition of the crime scene, one that is incontestable. First, take a picture that shows where the scene is; a shot with a street sign with the crime scene location in the background. Take pictures of the areas around the crime scene; alleys, dumpsters, rear areas, neighboring structures and even the structures across the street. Next, take pictures of the outside of the structure, showing points of entry and exit. Enter the structure, taking shots that show the locations and layout of the rooms. Take pictures of the whole room where the crime took place. Take close-ups of the scene or body. All pictures of items of evidence, which will be covered in the next paragraph, should be take both with and without a scale (a small ruler showing the size of the object). Take pictures with the scale to show the size of an object. Take pictures without the scale in case its presense in the picture blocks other evidence. What items are photographed at a crime scene? Bullet casings; photograph as a group and photograph individually. Photograph any dropped items, foot prints or animal tracks. If a homicide, photograph the body or bodies. Photograph any toolmarks, bitemarks or skin impressions. Basically, anything that might be evidence is photographed. Imprint evidence requires extra measures. Shoe imprints are photographed individually and as a series or group. Shoe imprints need to be lit from the side to show as much detail in the imprint as possible. Tire imprints are photographed from above as a whole. If the tire imprint is four feet long, then a picture showing all four feet is taken. Detail pictures are then taken showing one foot sections, each picture overlapping the one before it. This way, specific detail can be show and the overlapping pictures lined up to show the whole print. Again, all pictures are take with and without a scale. There is a special technique for no light situations. This technique is useful outdoors at night (perhaps a car accident scene), or in situations where the room is too big to light or there is no light available for pictures to be taken (such as a burnt out warehouse arson). The camera is set on a tripod with its shutter locked open. The photographer walks to several points in the room, popping off the flash, which is held in his or her hand. Each time the flash goes off, the film in the camera is exposed to another part of the room. The photographer does not appear as he/she is behind the flash and does not get exposed to the light when it pops off and only moves around the room while it is still dark. Remember, the film in a camera captures light. If there is no light, you can walk around in front of a camera all you want and never show up on the film. Video is also used to film crime scenes, taking long sweeping shots that take in everything in an unbroken time frame. The problem with video is, camcorder microphones will pick up the officers talking in the background, which can sometimes be embarrassing when the tape is replayed in court.