Principles of Crime Scene InvestigationThe key principle underlying crime scene investigation is a concept that has become known as Locard’s Exchange Principle. It states that whenever someone enters or exits an environment, something physical is added to and removed from the scene. This principle is generally summed up by stating: “Every contact leaves a trace.” Show
The logic behind this principle allows investigators to link suspects to victims, to physical objects, and to scenes. Any evidence that can link a person to the scene is referred to as associative evidence. This may include items such as fingerprints, blood and bodily fluids, weapons, hair, fibers and the like. This type of evidence answers the question “Who did this?” While associative evidence links people to the place of the crime, reconstructive evidence allows investigators to gain an understanding of the actions that took place at the scene. A broken window, a blood spatter pattern, bullet paths and shoe prints can all reveal what actually happened. This type of evidence answers the question, “How did it happen?” To help establish the linkage of people and things to a scene, the investigator may also collect known substances, called control samples. These can be items such as fibers from carpeting at the scene, glass fragments, soil, vegetation and other trace evidence. Learn more about trace evidence ▸ If these are found on the suspect’s clothing, in their vehicle or at their residence, it could provide circumstantial evidence linking the person to the scene. For example, police are called to a residential neighborhood where a home invasion and burglary has just occurred. Investigators collect glass fragments from a shattered cabinet door with a distinct pattern etched into the glass. A tip leads investigators to a local man with a known history of burglary. Examination of the suspect’s clothing yields glass fragments with the same distinct pattern as the smashed cabinet doors. Eliminating people who could not be the perpetrator is also important. Control samples of fingerprints and DNA are often collected from any person(s) who have access to the scene who are not considered suspects. Gauging the Value of EvidenceIt is unique - If an item is found that helps narrow the possibilities of who might be considered a suspect, or the manner in which a crime was committed, this evidence would be of use. Is an impression from a vehicle tire found in the dirt at the scene? The tread impression can be compared to others to determine the type of tire that was on the car. Is a shoe print left in the soil? The tread may help to identify the size and type of shoes it came from and the wear pattern could be used to match it to a specific pair. Learn more about footwear impressions and tire tracks ▸ It has a low probability of occurring by chance - Considering the mathematical probabilities will help to determine the odds that a piece of physical evidence found at the scene could appear merely by coincidence. If DNA evidence found at the scene matches a suspect, the chances are exceedingly low that another person could have left this sample. But even evidence that has a much higher probability—for instance, a common type of shoeprint that is left in the soil—is still valuable. When combined with other high probability evidence, these can help narrow the list of possible parties and build a compelling case. It is inconsistent - If an item is found that is out of place or inconsistent with the setting, or is out of character for the victim—for instance if the victim was a non-smoker but a cigarette butt is found at the scene—this could be an important bit of evidence. It is a physical match - If trace evidence is found on the suspect or in his possession that matches something at the scene, this makes this item valuable as evidence. For instance, broken plastic parts or a broken fingernail that can be matched by fracture marks can demonstrate that two pieces were once a part of the same item. Back to top of page ▲ Identification BasicsA very important step for the prevention of illegal sales to minors is adequate training of staff on what the policies and laws are regarding the sale of alcohol. Staff must know what to look for when checking ID’s to be able to prevent the sale. They must also know how to deal with the customer once a suspected false/counterfeit ID is presented. The legal drinking age in California is 21. You are never required to sell or serve alcohol to anyone. A person does not have a legal “right” to buy alcohol, but you have a legal right to refuse service to anyone who cannot produce adequate evidence of their age. If you have any doubts about an identification, you should refuse the sale of alcoholic beverages. However, it is important to remember that you cannot discriminate as to race, color, sex, religion, ancestry, disability, marital status, sexual orientation, or national origin, among other things. Persons under the age of 21 are not protected by age discrimination laws when it comes to the sale or service of alcoholic beverages. Bona Fide IdentificationBona fide (legally acceptable) identification is one card that contains these six characteristics:
Examples of Identification that could be bona fide
Examples of Identification that are not bona fide
A business may have a company policy that is stricter than the law; e.g., “Only California driver licenses/identifications are accepted” or “anyone purchasing alcoholic beverages MUST present an identification, regardless of age.” System for Checking IdentificationABC recommends you check identification in a methodical and systematic manner. A simple acronym to help people remember how to check identification and spot false or borrowed identification is by using the F-L-A-G system.
Sellers of alcoholic beverages should also ask customers to remove the identification from wallets/ID holders in order to physically handle the card. This will help to properly examine the identification. “F” = FEEL
Identifications may also contain security features such as:
“L” = LOOKTake your time looking at the identification in your hand. Know what to look for:
“A” = ASK QUESTIONSIf you suspect that an identification is fake, ask the ID holder questions. If they don’t know the answers or get nervous, you probably have a fake ID on your hands. Here are some questions you can ask the cardholder to help determine if their ID is fake.
“G” = GIVE BACKIf the identification passes the feel, look and questions tests, give it back to the customer and make the sale. If it does not, refuse the sale and then, either give the ID back or seize it, depending on your company’s policy. You have a right to refuse service to minors. If you seize an ID, here are the requirements per Section 25659 of the Business and Professions Code:
Good I.D. PoliciesThe following are some good ID policies:
Identifying Minors (and how they may try to fool you)Be aware that minors may look and act in ways to deceive you. Some minors may look or act young and others may look or act older to confuse you about their true age. Identifying Minors:
Laws Applying to False Document and Identification CrimesMisdemeanors are punishable by up to one year in county jail, while felonies are punishable by state prison time. California Vehicle Code Sections
Penal Code Sections
Business and Professions Code Sections
What do you call a list of people who have physical possession of the evidence?The chain of custody of evidence is a record of individuals who have had physical possession of the evidence.
What is the chain of custody a list of all people who had possession of the evidence?The chain of custody is a tracking record beginning with detailed scene notes that describe where the evidence was received or collected. Collection techniques, preservation, packaging, transportation, storage and creation of the inventory list are all part of the process used in establishing the chain of custody.
What is the chain of custody a list of all people?In practice, a chain of custody is a chronological paper trail documenting when, how, and by whom individual items of physical or electronic evidence—such as cell phone logs—were collected, handled, analyzed, or otherwise controlled during an investigation.
Why is evidence media write protected quizlet?Why should evidence media be write-protected? To ensure that data isn't altered. List three items that should be in your case report.
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