Transcript Slide 1
Legal Aspects of Evidence Chapter 6 Crime Scene Evidence, Experiments & Models Real Evidence Anything that can be perceived by the five senses (except trial testimony) is considered real evidence. All types of real evidence have two things in common They must be marked and formally introduced as evidence The attorney who wishes to introduce them must lay a foundation to establish the admissibility of the items in question Laying the Foundation The attorney requests that the clerk mark the .38 caliber gun as People’s No. 1. The prosecutor then calls the witness and lays the foundation to show that the gun is was found at the crime scene. Ballistics tests show that the slug test-fired from this gun matches the slug removed from the victim. Identifying Evidence Objects are often identified by the initials of the officer who found the item at the crime scene It is extremely important that these marks not be placed where they will be in the way when laboratory tests are done Fingerprints, traces of blood, etc., must be preserved on the object Chain of Custody Phillip Vanatter - LAPD The chain of custody accounts for everyone who had possession of an item of real evidence from the time it came into police custody until it has been introduced in court. Philip Vanatter is the LAPD detective who mishandled evidence by driving around LA with OJ Simpson's blood in his pocket. Evidence Label Sketching the Location of Evidence Before collecting and packaging evidence, the officer should make a detailed record of the crime scene, with clear indications where each item was found. Sketches should be to scale including locations of all doors, windows, and furniture. Points of the compass should also be included. Photograph the Evidence When taking photographs of evidence, make sure there is something in them that clearly indicates the size of the items shown. A ruler is frequently placed near the object that is the focus of the picture for this purpose. Types of Cases Using Scientific Evidence 60-80% drugs or fingerprints Firearms, blood, bloodstains, and semen Murder and drug possession Scientific Basis for Fingerprint Identification The scientific basis for fingerprint identification refers to the fact that fingerprints are: Unique - an individual characteristic – no 2 people have the same fingerprints Permanent - Fingerprints remain the same over a person’s lifetime and Have ridge patterns that can be systematically classified Fingerprint Identification Fingerprints that are recovered from the crime scene or from other evidence are called latent (not visible) prints A detailed explanation of how the latent prints were recovered is usually required Prints on hard, non-absorbent surfaces were recovered by applying fingerprint powder to the surface with a camel-hair brush The powder sticks to the skin oil and makes the print visible Fingerprint Patterns Tented Arch Double Loop Plain Arch Loop Whorl Central Pocket Loop Laying the Foundation for Scientific Evidence Three questions must be answered to lay the foundation for scientific evidence Is this a valid scientific test? Was accurate equipment used for the test? Was the test performed in an appropriate manner by a qualified person? Scientific Evidence Fingerprint comparisons are a good example of a well established test Expert witnesses will be called to provide the necessary background on the test and explain the necessary principles behind it Blood Alcohol The most common use of blood alcohol testing is in drunk driving cases Blood alcohol is also used in cases where the defendant’s sobriety may have a bearing on criminal intent The most common test for alcohol is done on breath samples Blood Typing Blood typing is done on human blood ABO system is most common A = 41% of US are type A B = 10% of US are type B AB= 4% of US are type AB 0 =45% of the US are type 0 Blood typing cannot be used to conclusively show that blood came from a specific suspect DNA Testing Every individual’s DNA is unique (*except for identical twins) DNA testing can be performed on a blood stain the size of a quarter or a semen stain the size of a dime to determine if the evidence found at the crime scene matches samples extracted from the suspect DNA testing can also be performed on hair. DNA Testing DNA testing is admissible in all states. DNA from a semen sample (found at the crime scene) can be matched to a blood sample taken at a clinical laboratory. DNA samples can be contaminated by bacteria, virus, detergents, cleaning fluids, and contaminated lab equipment. Identification of Controlled Substances Lab analysis often plays a major role in drug possession, distribution, and manufacturing cases Qualitative and quantitative chemical analysis is performed on the drugs Infrared spectrophotometry is used frequently because it is the least expensive and easiest to use Identification of Firearms Firearms can be identified from their fired bullets and cartridges Pistols, rifles, assault rifles, and machine guns are “rifled” firearms Rifled refers to the spiraling lands and grooves of the weapon’s barrel, which leave marks (striations) on the bullets as it is discharged Identification of Firearms Before testing a weapon for identification purposes, it should be examined for latent prints, blood, bits of skin, and trace evidence. Examination of the weapon should include the model, manufacturer, type of weapon, caliber, serial number, number of shots, and barrel length. Tests Not Commonly Accepted Hypnosis Polygraph Neither hypnosis nor polygraph examination are widely accepted in court. Experiments Conditions must be similar to those that existed when the event in question occurred Experiments must be based on sound scientific principles The judge may refuse to admit experimental evidence if he feels it will be too confusing to the jury or if it will take up too much time Models, Maps, & Diagrams Computer simulations, diagrams, and animated videos are becoming more popular in court Maps that are relevant and to scale are usually admissible.