forensic science speech

i did a speech on forensic science. here are my notes: 1. A perimeter is taped off with barricade tape in order to keep only those necessary on site. This is done to prevent Contaminated Evidence. 2. Photographs of all evidence are taken before anything is touched, moved, or otherwise further investigated. Evidence markers are placed next to each piece of evidence allowing for organization of the evidence. Sketching the scene is also a form of documentation at a crime scene. This allows for notes to be taken as well as to gauge distances and other information that may not be easily detected from only a photograph. The investigators will draw out locations of evidence and all other objects in the room. The sketch is usually drawn from an above point of view. Notes are taken by investigators to ensure memorization of their thoughts and suspicions about different pieces of evidence. Videos are taken as well 3. Evidence is collected through two ways: forensics and interviews. All forensic evidence is bagged separately to prevent any cross-contamination. Forensics uses a variety of different tools and techniques. Fingerprint collection through the use of grey or black magnetic powder. DNA and other bodily fluids are collected and, whether it is hair or fluid, for further examination in a lab. Shoe and tire prints can be collected using dental stone. Electronics are taken for examination by a technical expert to search for further evidence. Documents from the area are also taken for further examination. Ammunition and weapons are taken for matching to wounds and ballistics. Photographs of tool marks are taken because they can be matched to a weapon at a later time. Any other trace evidence is also collected. Trace evidence is anything left behind by a perpetrator or could have been transferred to the perpetrator. Interviews of both witnesses and victims of the crime are taken by law enforcement officials in order to gain knowledge and creating a timeline of events. 4. Different types of crime scenes include outdoors, indoor, and conveyance. Outdoor crime scenes are the most difficult to investigate. The exposure to elements such as rain, wind, or heat, as well as animal activity, contaminates the crime scene and leads to the destruction of evidence. Indoor crime scenes have a significantly lower chance of contamination because of the lack of exposure. The contamination here usually comes from the people factor. Conveyance crime scenes are crimes committed by means of transportation, such as robbery or auto theft. Each type of crime scene, along with the nature of the crime committed (robbery, homicide, rape, etc.) have different procedures. 5. Crime scene reconstruction is the use of scientific methods, physical evidence, deductive reasoning, and their interrelationships to gain explicit knowledge of the series of events that surround the commission of a crime. People ON the scene: 1. Police officers are typically the first to arrive at a crime scene. They arrest the perpetrator is he's still there and call for an ambulance if necessary. They are responsible for securing the scene so no evidence is destroyed 2. The CSI unit documents the crime scene in detail and collects any physical evidence. 3. The district attorney is often present to help determine if the investigators require any search warrants to proceed and obtain those warrants from a judge. 4. The medical examiner (if a homicide) may or may not be present to determine a preliminary cause of death. 5. Specialists (entomologists, forensic scientists, and forensic psychologists) may be called in if the evidence requires expert analysis. 6. Detectives interview witnesses and consult with the CSI unit. They investigate the crime by following leads provided by witnesses and physical evidence. Taking fingerprints: Tools for recovering fingerprints include brushes, powders, tape, chemicals, lift cards, a magnifying glass and Super Glue. A crime lab can use fingerprints to identify the victim or identify or rule out a suspect. There are several types of prints a CSI might find at a crime scene: Visible: Left by the transfer of blood, paint or another fluid or powder onto a surface that is smooth enough to hold the print; evident to the naked eye Molded: Left in a soft medium like soap, putty or candle wax, forming an impression Latent: Left by the transfer of sweat and natural oils from the fingers onto a surface that is smooth enough to hold the print; not visible to the naked eye A perpetrator might leave prints on porous or nonporous surfaces. Paper, unfinished wood and cardboard are porous surfaces that will hold a print, and glass, plastic and metal are non-porous surfaces. A CSI will typically look for latent prints on surfaces the perpetrator is likely to have touched. For instance, if there are signs of forced entry on the front door, the outside door knob and door surface are logical places to look for prints. Breathing on a surface or shining a very strong light on it might make a latent print temporarily visible. When you see a TV detective turn a doorknob using a handkerchief, she's probably destroying a latent print. The only way not to corrupt a latent print on a non-porous surface is to not touch it. Proper methods for recovering latent prints include: Powder (for non-porous surfaces): Metallic silver powder or velvet black powder A CSI uses whichever powder contrasts most with the color of material holding the print. He gently brushes powder onto the surface in a circular motion until a print is visible; then he starts brushing in the direction of the print ridges. He takes a photo of the print before using tape to lift it (this makes it stand up better in court). He adheres clear tape to the powdered print, draws it back in a smooth motion and then adheres is to a fingerprint card of a contrasting color to the powder. Latent fingerprints and impressions: Develop latent fingerprints; analyze and compare fingerprints, footwear and tire impressions; run fingerprints through the Automated Fingerprint Identification System (AFIS, which utilizes the FBI database) for comparison against hundreds of millions of prints Footwear Impressions and Tool Marks A latent fingerprint is an example of a two-dimensional impression. A footwear impression in mud or a tool mark on a window frame is an example of a three-dimensional impression. If it's not possible to submit the entire object containing the impression to the crime lab, a CSI makes a casting at the scene. A casting kit might include multiple casting compounds (dental gypsum, Silicone rubber), snow wax (for making a cast in snow), a bowl, a spatula and cardboard boxes to hold the casts. If a CSI finds a footwear impression in mud, she'll photograph it and then make a cast. To prepare the casting material, she combines a casting material and water in a Ziploc-type bag and kneads it for about two minutes, until the consistency is like pancake batter. She then pours the mixture into the edge of the track so that it flows into the impression without causing air bubbles. Once the material overflows the impression, she lets it set for at least 30 minutes and then carefully lifts the cast out of the mud. Without cleaning the cast or brushing anything off it (this would destroy any trace evidence), she puts the cast into a cardboard box or paper bag for transport to the lab. For tool mark impressions, a cast is much harder to use for comparison than it is with footwear. If it's not feasible to transport the entire item containing the tool mark, a CSI can make a silicone-rubber cast and hope for the best. There are two types of tool marks a CSI might find at a crime scene: Impressed: A hard object contacts a softer object without moving back and forth (for example, a hammer mark on a door frame). The tool mark is an impression of the tool's shape. It's difficult to make a definite match with an impressed tool mark. Striated: A hard object contacts a softer object and moves back and forth (for example, pry marks on a window frame). The tool mark is a series of parallel lines. It's easier to make a definite match with a striated tool mark. ­In tool mark analysis, the lab might determine what sort of tool made the mark and whether a tool in evidence is the tool that made it. It can also compare the tool mark in evidence to another tool mark to determine if the marks were made by the same tool.