Crimes and Forensic Chemistry
Basic information:
Forensic science uses science principles, techniques and methods to the investigation of crimes (for example a detective wants to prove someone was present at the location of a murder).
When a crime is investigated,evidence is collected, analyzed, interpreted and later presented in court
Evidence samples can include things like fingerprints, hair, a smear of blood,gunshot residue.
There are a large range of specialist fields in forensic science such as forensic pathology, forensic toxicology, forensic chemistry, DNA analysis, forensic entomology, and more.
DNA analysis and profiling can link a suspect to a crime scene. DNA is a molecule that determines how our bodies are built, it is found in all body tissues and everyone (except identical twins) has unique DNA (=deoxyribonucleic acid).DNA is considered an individual characteristic that exclusively links e.g. a hair sample to a single origin (= to a specific person). However, it is not easy because 99.9% of human DNA is the exact same in every person and only 0.1% or even less is unique.
In the case of forensic entomology, scientists examine insects found in and around human remains to determine the time of death
Forensic toxicology studies the effect of drugs and poisons on the human body in relation to medical and legal situations.
The famous fictional character Sherlock Holmes used forensic science as one of his methods for investigating crimes.
Examples of forensic science can be found throughout popular culture, including TV shows such as CSI, Bones, NCIS, Law & Order and the Mentalist, which all use forensic science as part of their story lines.
A)Crimes and criminals
Crime=activity that is against the law, an illegal act for which someone can be punished by the government. There are many types of crimes, for example a theft, shoplifting, joyriding, robbery, burglary, arson, forgery,assault, kidnapping, homicide, rape, murder, drink-driving, drug dealingand some others. (more serious ones x less serious ones, suitable forms of punishment:penalty, imprisonment…)
Criminal = a person who has committed a crime or who has been proved to be guilty of a crime by a court.
Suspect = a person who is believed to be guilty of committing a crime
Victim = a person who has been attacked, injured, robbed or killed by a criminal
Eye witness = a person who sees something (such as a crime) happen
B)Investigating a crime (Forensic Science)
It involves the study of facts that are used to identify, locate and prove theguiltof an accused criminal.
Criminal investigation is an ancient science that may have roots as far back as c. 1700 BC in the writings of theCode of Hammurabi. In the code it is suggested that both the accuser and accused had the right to present evidence they collected. Modern-day criminal investigations known asforensic science is mostly done by government police forces. When a serious crime is investigated, the investigation process typically consists of four steps:
a) physicalevidence is collected at the crime scene by police officers or crime scene investigators
b) the physical evidence is analyzed by forensic scientists (often chemists) in a laboratory
c) all the evidence (that means the analyzed physical evidence + other evidence /=eye witness stories , police reports, crime scene sketches and interrogation,etc./ )is interpreted by detectives
d) evidenceis presented in court
Most forensic scientists analyze evidence in a crime laboratory and spend little time at the crime scene. The duties of forensic scientists are not exactly as they are portrayed on many popular TV shows, where the crime scene investigator plays the role of Sherlock Holmes and does everything from collecting the evidence to solving the crime. In real life a team of experts does the job of television’s crime scene investigators. The forensic scientists do not directly solve crimes; they simply analyze the physical evidence in a crime laboratory
C)Forensic Chemistry
A large number of forensic scientists are chemists. Forensic chemists employ their knowledge of chemistry to analyze evidence such as fibers, paint, explosives, charred debris, drugs, glass, soil, documents, tool marks, and firearms. To a lesser extent, forensic chemists also use their knowledge of toxicology (=the study of poisons and their effects), fingerprints, footwear impressions, tire impressions, and hair analyses. The forensic chemist does not typically analyze biological evidence or carry out DNA analyses. These analyses are typically performed by a forensic biologist.
After a police officer has collected evidence at a crime scene, the evidence is brought to the crime lab for a forensic chemist to analyze. The chemist follows a specific process, based on the scientific method, for analyzing evidence.
Samples collected from a crime scene are called questioned samples(because the identitiesand origins of those samples are unknown). In order to draw conclusions about the identity or origins of questioned samples, the forensic chemist will need known samples as a reference. A known sample might be collected as part of the evidence—for instance a hair sample collected from a suspect.
Forensic analyses may be performed to (1) identify a questioned sample or (2) compare a questioned sample to a known sample for the purpose of determining the source or origin of the sample (where it came from).
Fingerprint detectionand fingerprints analysts
Fingerprints left at crime scenes are one of the tools used to incriminate or eliminate suspects. However, they’re not always visible, and investigators will often rely on chemical techniques in order to visualize them. Some fingerprints are visible to the naked eye, so they canbe recorded simply with the aid of photography and no further work is needed. There are also latent prints left on surfaces due to the natural oils and sweat from the skin which can´t be seen unless something is done to make them visible.
There are about 20 effective techniques used in fingerprint labs to make latent prints visible. Some of these techniques, such asninhydrin,diazafluorenoneandvacuum metal deposition, show great sensitivity and are used operationally. Some fingerprint reagents are specific, for example ninhydrin or diazafluorenone reacting with amino acids. Others such asethyl cyanoacrylatepolymerisation, work apparently by water-based catalysis and polymer growth. Vacuum metal deposition using gold and zinc has been shown to be non-specific, but can detect fat layers as thin as one molecule. More mundane methods, such as the application of fine powders, work by adhesion to sebaceous deposits and possibly aqueous deposits in the case of fresh fingerprints.
D)Other subspecializations of forensic chemists
With the wide variety of evidence that may be analyzed by the forensic chemist, subspecialization is also quite common -firearms analyst, trace evidence analyst, fingerprint analyst, or drug chemist. Because more than 70% of all evidence is drug related, drug chemists are quite common in crime laboratories.
Meet a forensic chemist – an interview with Melisa Valadez
Q: What activities do you perform regularly at in the crime lab?
A: I work in the trace evidence section of a crime laboratory and analyze evidence such as hairs, fibers, paints, shoe and tire impressions, physical matches, and vehicle lamp filaments. Most of my work is done in the lab using microscopes and other instrumentation, but sometimes I am asked to collect evidence from crime scenes as well. I also travel across the state in order to testify in the court of law to explain my procedures and conclusions to juries.
Q: What is your educational background?
A: I have a Bachelor of Science in Chemistry from Texas A&M University and a Master of Science in Forensic Science (MSFS). Once I was hired as a forensic scientist, I went through an extensive in-house training program prior to working on any cases. Since then I have attended numerous conferences and training classes in order to further my knowledge.
Q: What do you like best about your job?
A: There is so much variety in what I do on a daily basis. Each case that comes in has its own story, and each item of evidence has to be handled in its own unique way. I get to do something different every day, and my knowledge base is constantly expanding. One day I might be working on a homicide case with bloody shoe impression evidence and the next day it may be a criminal mischief case involving paint. You just never know where each case will take you.
Q: How does what you do compare to what is portrayed on crime shows like CSI?
A: The most obvious difference is that we can’t solve cases in an hour. We may work on one case for months and still only be able to provide investigators with minimal information. In other cases, it might take only a single day to provide all the information that investigators need to wrap up the investigation. Another big difference is that most of our work is done in the lab. Occasionally we will process a scene and collect our own evidence, but most forensic scientists stay in the lab. The investigation side and the forensics side are usually kept separate and are dealt with by separate entities. The law enforcement agencies, the attorneys, and the laboratory staff all keep in contact and work closely together in order to see a case through to the end.
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