Forensics Flashcards
What is forensic science?
The application of scientific methods and techniques to matter under investigation by court of law. It is used to support legal decision making by providing evidence.
What is Locard’s principle?
Every contact leaves a trace
What is meant by physical fit?
Comparing two items that were once part of a single item- can be used to prove beyond reasonable doubt the connection between a crime and a suspect. e.g. glass shards that fit together, paint the has scraped off a car at the crime scene
What is trace evidence?
Very small amounts of material that provide a link to someone or something e.g. blood, hair, DNA, clothing fibers, paint, soil.
What is the difference between inceptive evidence and reactive evidence?
Inceptive evidence is finding evidence that paints a picture of a perpetrator
Reactive evidence is finding evidence that links to a suspect
What factors make trace evidence more valuable?
A large amount of material- a lot to analyze, how persistent the material is- how well the material sticks, evidence value- how rare the material is.
How can trace evidence be recovered?
Many different techniques such as brushing, taping, shaking, vacuuming, swabbing, pipetting, hand picking and extracting.
How can glass be analyzed?
Glass can be analyzed and matched by color and thickness, physical analysis, or chemical analysis using a scanning electron microscope (SEM) or energy dispersive x-ray analysis.
What information can glass craters give about bullets?
Glass shards can have the physical fit principle applied. The wider side of the crater is the side the bullet exited, if multiple bullets have pierced glass, the order of impact can be determined by the intersecting cracks.
What are fibres?
Any long thin flexible solid object, that is longer than it is wide. Some fibers are more rare than others so have more strength in court.
How can fibers be collected and analyzed?
Fibers can be collected through taping, and analyzed by looking under a microscope. Thin layer chromatography can give information on the dyes in fibers. Infrared spectroscopy can be used on artificial fibres.
How is hair analysed?
Hair can be identified as human or animal hair, the area of the body where hair came from can be identified, the race of the host can be identified, any artificial altercations such as die can be seen.
How can common bodily fluids like semen and saliva be analysed?
Semen can be identified under a microscope, or by looking for acid phosphatase, or by looking for p30 which is in seminal fluid so is useful for sterile individuals. Semen has DNA so can undergo DNA analysis.
Saliva may have traces of DNA from cheek cells, it can be tested for by starch/iodine or salivary amylase.
How can blood be used for analysis?
Blood can be classified into animal or human blood, blood group and type, and sex, age and race of the source. Red blood cells and platelets have no DNA but white blood cells do.
How can a crime scene be checked for blood?
Through visual analysis, but blood may have been wiped or cleaned. Leachomalachite green or the kastle meyer test can be used to test for blood. LMG is oxidised and becomes green or phenolphthalein is oxidized and becomes pink. Luminol can be used to test for the presence of haemoglobin and can be seen under UV light. Luminol + H2O2 = 3 aminophthalate (produces UV)
How can the pattern of blood be analysed?
Blood pattern analysis can give information about the sequence of events of a crime. This can be used to create a timeline and give information about the position of the victim and evidence of struggle. This can be matched against witness statements.
What are the different types of blood pattern?
Passive: drops due to gravity, pools. Not related to movement. The shape of the drops is effected by the target surface.
Transfer- wet bloody surface transfers blood to another surface- smear/ wipe. Indicates movement.
Projected- Active blood splatters can come from an arterial gush, or can be cast off stains from a weapon which can tell about the velocity of the impact and the point of convergence.
How is the value of trace evidence determined?
How much evidence there is, what the rarity of the evidence is, the combined amount of trace evidence, the presence of alternative innocent sources, how reputable the trace evidence is (how much it links to a single person), how relevant it is to the crime and how well funded the analysis has been.
What is the difference between pharmacodynamics and pharmacokinetics?
Pharmacodynamics relates to what a drug does to the body. It is the study of the biochemical, physiologic and molecular effects on the body, involving receptor binding, post receptor effects and chemical interactions.
Pharmacokinetics is what the body does to a drug, it is the movement of the drug through the body and eventually out. The time course of its absorption, distribution, metabolism and elimination.
What is the path of absorption and distribution of alcohol?
Alcohol is ingested through the most, goes down the esophagus into the stomach and small intestine where it is absorbed into the circulatory system and distributed amongst the all organs of the body including the brain, kidneys, lungs and liver.
What is alcohol metabolism?
The process in which the body breaks down alcohol and eliminates it, most of this is done in the liver.
How quickly is alcohol absorbed?
Alcohol is absorbed between 15-45mins after consumption. The absorption rate depends on quantity, concentration, contact time in the GI tract, food and stomach emptying time.
How much alcohol is distributed to each organ?
The amount of alcohol distributed to each organ is proportionate to the water content of each organ. The alcohol in the organs reaches equilibrium with the alcohol in the bloodstream.
What effects do blood alcohol levels relate to?
Under 50- not obvious
50-100- tipsy, slurred speech, bravado
100-150- abnormal walking pattern, some nausea
150-200- nausea, non co-operative
200-300- probable coma
300-400- coma, impaired respiration
400+ death from respiratory paralysis
How much alcohol is metabolized and what is the rate?
90% of alcohol is metabolised, the rest is excreted directly. Blood alcohol level is reduced by around 18mg/hour but can range between 9-27. The variance in rate is due to genetics- it depends on which alcohol dehydrogenase isozyme you have. The rate of metabolism does not change with the addition of reduction of alcohol- zero order kinetics.
What is the pathway of alcohol metabolism?
Alcohol is typically broken down into acetaldehyde by alcohol dehydrogenase (rate determining) and then into carbon dioxide and water by aldehyde dehydrogenase. There is two other rare metabolism paths for alcohol: the catalase pathway and the cytochrome p450 pathway. The cytochrome pathway produces free radicals that damage the liver but is typically only used when alcohol dehydrogenase is saturated.
What is legal driving blood alcohol conc in all nations in UK and how is this converted to breath alcohol?
50mg in Scotland, 80mg in the rest. Divide by 2300 for breath alcohol. Times by 1.3 for urine alcohol.
What are the accuracies of measurements of alcohol concentration?
Blood is the most accurate, it is a measurement of the amount of alcohol effecting the brain. Urine only provides a mean value over the period of excretion. Breath alcohol is in equilibrium with blood, is useful for roadside tests but does not provide evidence.
How can alcohol be analysed
By biochemical analysis: ADH requires a co-enzyme (NAD+) to oxidize alcohol. This reduces the co-enzyme (NADH) which can be measured to find BAC by calorimetrically or spectrophotometrically.
Chemical: by electrochemical fuel cell breathalyzers, which are used to make arrests so more accurate tests can be carried out such as infrared optical sensor breathalysers.
How does an electrochemical fuel cell work?
Alcohol breath passed through a tank from an anode (-) to a cathode (+). The rate of positive ions, directly related to alcohol concentration, changes depending on increasing concentration. Some ions are captured in the electron rich pads either side, which is dependent on breath alcohol conc, so it can give a reading.
How does an infrared optical sensor work?
Infrared waves are passed through a tube. Alcohol breath is blown into the tube and the alcohol blocks some infrared allowing the infrared to be measured at the end of the tube and give a measure of BAC.
What is forensic toxicology?
The study of the effects of alcohol, drugs or poisons with application to the law. This is involved in post-mortem toxicology, human performance and drug testing.
What is paracelsus’ third defence?
Everything is poison depending on the dose. All substances can harm the body if a large enough dose is taken.
What is a controlled drug?
A drug which the manufacture, possession and use of is controlled by the government. Drugs are separated into classes based on their danger to society, the higher the class the more severe the sentence.
What are temporary class drugs?
New drugs with 1 year temporary bans put on them to allow the government to assess the danger of the drug and classify it. These new drugs often have similar chemical structures to others and provide legal highs.
What are the different types of drugs?
Stimulants: drugs that stimulate brain activity in the prefrontal cortex e.g. cocaine, amphetamines
Depressants: drugs which inhibit brain activity e.g. alcohol, heroin
Hallucinogens: drugs which induce alterations in perception and mood e.g. LCD, mushrooms, cannabis, MDMA
How can drugs be analysed and what information can this tell you?
Drugs can be analysed through presumptive tests such as dipstick urine tests, or accurately through chromatography to identify drugs through their weight and charge. Mass spectrometry, immunoassays or spectroscopy can also be used. This can tell you what drugs are present in a sample, and can produce unique chemical signatures that link them back to gangs.
How can gas chromatography be used to analyse a drug?
Gas chromatography separates the individual components of a drug based on weight and charge and shines infrared light through this to produce a graph of peaks. These peaks are different depending on the weight and polarity giving each drug a unique signature. This can also identify contaminants.
Why is hair analysis often used in workplace drug testing?
Hair traps drugs in the base of the cells- melanin and stays present in the hair as it grows. This hair can then be heated and traces of drugs such as cocaine and heroin can be found. Urine and saliva testing only gives a recent profile.
