Forensic science%20from%20fingerprints%20to%20 dna
Pascal Goetgheluck/Science Photo LibraryForensic – science from The forensic team must collect as much evidence as isfingerprints possible from the crime scene. to DNAIn the bedroom of 10 Main Street, Murrundrongo,a man in his fifties lies dead on the floor next toa bed . . . . . . with a broken glass bottle nearby; reddish-brown stains on the The man may have died of natural causes, the stains could be from spilt walls, a red stain on the carpet and red wine, and a cricket ball may have the bathroom window smashed. smashed the bathroom window weeksRoger Beckmann What’s been going on – accident or ago — or even after the death. foul play? To put the pieces together, a team This is the sort of puzzle that could effort is required. Police officers will confront a crime scene investigator interview neighbours and gather (CSI) from the police force. Crime information about the dead person. scene investigators, often referred A doctor, or forensic pathologist, may to as ‘scientific police’, are one part be called to examine the body. The of the forensic team whose skills are police forensic team must look for essential in modern police clues as to what occurred, and try to investigation. In the fictitious scene reconstruct a possible sequence of just described, police must determine events. whether or not a crime has occurred.
The science of crime material using the observations, measurements, physical evidence Every day, many crimes are committed and photos collected by the CSIs. in Australia. To solve these crimes They conduct: effectively – so that criminals are • chemical analysis of paint, glass, brought to justice – the police need to fibres, accelerants (substances work very efficiently, using as many used to start a fire), explosives techniques as possible. Science has (from discharged guns), inks and become an essential tool for the printer toners; modern police force. • biological analysis, which includes Originally, the word ‘forensic’ meant analysis of DNA, body fluids, anything relating to a law court. But fingerprints and swabs; today it refers to a whole new subject. • document examination, which Forensics or forensic science means involves examining hand-writing, using science to solve crime. But what handwriting impressions (eg. from exactly does a forensic scientist do? a note written on top of a pad The work of a forensic scientist falls of paper), machine-generated into three broad groups: field, documents, and paper and ink laboratory and medical. types; and Field workers or CSIs attend the • ballistics, which is the study of scene of a suspected crime, record in firearms and ammunition, and the detail what is present, and collect as identification of particular firearms much evidence as possible – without from fired cartridge cases and contaminating the scene in the bullets. Ballistics also involves process. They search for marks left by calculating the direction and AFP Forensic Services. implements such as crowbars, knives distance that a bullet travelled. or screwdrivers, or impressions from Another type of lab work in some shoes and vehicle tyres. CSIs also police forces is toxicology. This means investigate fires, explosions and illegal detecting and identifying drugs and drug laboratories. poisons, and determining their effects The lab-based forensic scientists on the body. begin their painstaking analysis of Science has become an essential tool for the modern police force. Analysis of objects determine if they were used in a crime. The third area of forensic science – medical – is usually beyond the scope of police teams. Specialists areAFP Forensic Services. brought in as required. Forensic pathologists are most frequently used, Searching for evidence that may help solve the crime. but there are also forensic dentists (to identify teeth and bite marks) and forensic psychiatrists. The medical experts use their skills to gain evidence about causes of injury and death, or about the identity, behaviour and motivation of a criminal. Occasionally, other specialists may be used. Botanists may be called upon to identify pollen types found on clothing, while engineers may give advice on machinery, building collapses or major fires. A recent development in forensic science is information technology, which means using knowledge of computers and software. As such, police will often look for information on a suspect or victim’s computer. New forms of crime – so-called cybercrime – are making use of computers as criminal tools, for example to acquire information illegally by ‘hacking’.
Four main uses of forensics determine which areas to concentrate Is it like the TV their investigation on. For example,In Australia, the police characterise four they may use luminol, which detects shows?main uses of forensic investigation. traces of blood by reacting with the Forensic scientists are quick to pointThese are: iron in the haemoglobin molecules out that TV dramas about their work1. To prove an element of an offence, for that are within red blood cells. Luminol are inaccurate. example, to identify a substance as glows when it comes into contact with The most common misconception an illegal drug. blood. Sometimes it reveals small is that most forensic work is involved2. To associate or disassociate a traces of blood that would normally with murders. Instead, it is involved suspect from a crime scene or crime be invisible. with house burglaries, drug offences, exhibit (for example, a weapon). The presence of blood, however, fires and vehicle accidents. Secondly, does not mean it is from a human, or it is not the forensic experts’ job to3. To help determine a possible, or even that it had anything to do with a probable, sequence of events. confirm what police investigators would crime. After all, people do occasionally like to hear. Forensic science, like any4. To provide criminal intelligence, which cut themselves, which could leave form of science, involves having an means to give extra information to the a tiny drop of blood on the carpet. open mind and being impartial. police that may be used in the future. In the case of the smashed window The crime scene investigator or the For example, if illegal drugs are at Number 10, the investigators lab scientist cannot afford to hang on seized, careful analysis shows a discovered traces of blood on the to pet theories or preferred suspects. chemical ‘signature’ which may reveal shards of glass, but the stains on He or she must work to uncover facts what country or illegal laboratory the bedroom wall, and the liquid on that can be used as evidence. Quite produced them. This may help with the carpet, were not from blood. often, these facts may serve to rule other investigations. out many of the suspects that the police have. Finally, TV dramas tend to roll all Meanwhile, back at 10 Main Street, forensic work into one person’s the crime scene investigators will thoroughly examine the area where the Increasingly, responsibilities. In real life, forensic scientists are specialists. No single body was found. They will take detailed notes and photographs, look for CSIs are using person possesses all the knowledge and expertise of every field of fingerprints, palm prints and sole prints; marks of tools and weapons; specialised forensics. Solving crimes is very much teamwork, and modern teams are marks from shoes; fibres from clothing or material; fragments of paint and techniques large. glass and body fluids. Increasingly, CSIs are using specialised techniques, on site, to on site. The cast of CSI (Crime Scene Investigation) AFP Forensic Services. WIN Television Laboratory based forensic employ a number of accurate scientific techniques.
WIN Television Jorja Fox from CSI, fires a gun to compare marks on the bullet and shell. Answers from the dead Pathology is the study of disease, and cause of death. A forensic pathologist specialises in examining dead bodies to determine how and Constantino Margiotta/Science Image Library. when death occurred. As well as examining the body, either on site or through photos taken at the scene, the forensic pathologist may also use x-ray imaging and will usually conduct an autopsy or post-mortem. A post-mortem is a careful dissection of the corpse, which comes from the Latin language meaning after-death. The pathologist will also take samples of body tissues, like blood, liver or hair, for further analysis. The corpse may reveal what caused a person’s death. One of the first tasks with a body evidence, linking a suspect to the on site is to establish the time of crime. The remnants of explosive death. The pathologist starts with material from a gunshot may also be temperature. The normal temperature o present on the skin, for example, near inside a human body is 37 C. a bullet hole. Such residues, and A pathologist will take the temperature the bullet wound itself, can give inside the body, as well as the information about the type of bullet temperature in the place where the used, as well as the distance and body was found. The rate at which direction from which it was fired. body temperature falls after death At the autopsy, pathologists start depends on the external temperature, with carefully looking at the body and the clothing worn, the size of the body, its clothing. They then examine the and its percentage of fat. skin — looking for cuts, scratches, After 12 hours, most dead bodies stabs, wounds or injection needle are the same temperature as their marks — and the nails. surroundings, therefore other methods The body found at Number 10 had are required for determining the time a long thin scratch on the shin of the of death. There are many gradual right leg, and had been dead for about changes that take place after death. eight hours before police arrived in the These occur in a particular sequence, morning. concluding with total decomposition. Skilled pathologists can usually use these changes to assess, roughly, Secrets from within when death occurred. Although a body does not always After the dead body has been show marks on the outside, there is examined at the scene, it is wrapped often evidence inside that will be for transport. This is done very revealed during the autopsy. In our carefully because small details — like scenario, the pathologist found the fragments of skin, hair or blood caught back of the man’s skull cracked, under a victim’s fingernails during a and a pool of blood inside the skull. struggle — may provide crucial
An escape of blood from the bloodvessels like this is called ahaemorrhage. This type of internalbleeding can be fatal, as the pressureof the leaked blood damages thebrain. There are other clues within a bodythat can show up during an autopsy.For example, a large blood clot withina major artery or vein, or even in theheart itself, may be a cause of naturaldeath, which would rule out foul play. Samples of a person’s stomachcontents can reveal the last foodeaten. Blood analysis will show theexistence of any poisons, illegal drugsor medicines. Urine in the bladder may AFP Forensic Services.also be analysed. Analysis of the blood from the bodyfound at 10 Main Street showed a highconcentration of alcohol. Stomachanalysis revealed the remains of redwine and spirits. Also, damage to theliver was a telltale sign that the DNA fingerprinting has become a powerful tool in helping solve crime.deceased had been a heavy drinkerof alcohol. New prints are taken by a laser- DNA analysis does not enable scanning procedure, where the hand scientists to build up a picture ofPrint precision is placed on a flat glass plate, and its a person from their DNA. The only print is stored and compared to other characteristic that the DNA tells us isAnalysis of fingerprints is probably the prints electronically. the sex of the person. DNA profiling ismost well known use of forensic A new form of identification relies only used to compare different DNAscience. Each fingertip has a pattern on DNA, which carries the genetic samples, and to determine whether orof fine skin ridges that are slightly information of each person. Everyone’s not they could be from the samedifferent for every person — even DNA is different (except for identical person.identical twins. twins). DNA profiling or typing is sometimes called DNA fingerprinting because it allows police to identify Putting it all an individual in the same way as together fingerprints do. DNA can be extracted In our investigation of Number 10, from any body fluid (blood, saliva, blood found on a shard of glass from sweat, nasal mucus etc) or from the broken window yielded DNA fragments of a body (hair roots, identical to the dead man. The scratch torn skin or flesh). on his shin was recent, and probably Forensic scientists do not look the source of the blood on the glass. at the whole of a person’s DNA The sticky red liquid on the carpet sequence, but rather a sub-set — a was found to be port wine, some of DNA profile. DNA profiles are a very which was also found on the broken powerful means of determining bottle. The source of the wall stains whether two or more samples may or could not be determined, but they were Everyone has a unique set of fingerprints. may not have come from the same not caused by blood. person. If DNA profiles do not match, Police interviewed neighbours they came from different people. separately, and their statements A fingerprint is composed of grease However, if they do match, there is confirmed that the man, a heavyand dried sweat left behind by the tips still a very slight chance that they drinker, often arrived home late atof the fingers. The palms of the hand may have come from different people. night and had difficulty finding (andalso leave identifiable prints, as do the DNA is the same in every cell of the using) his keys. Sometimes he evensoles of the feet. body, and stays the same throughout tried to bang down his own door, Fingerprints can be detected on a life. As such, DNA profiles taken at or else fall asleep in the bushes.vast range of different surfaces using different times and places can be On the night he died, someone hada variety of techniques. The police compared in order to determine heard his drunken singing. It waskeep a huge national database of whether or not they come from the probable that he broke the window toprints taken from charged criminals. same person. gain entry to his own house, as it was too cold a night to stay outside. TheDNA analysis does not enable forensic evidence suggested that, while drunk, he fell onto a metal radiator near his bed and died fromscientists to build up a picture the blow to his head. The bottle that he was holding, broke as a result ofof a person from their DNA. his fall.
AFP Forensic Services.Counting crimeAcross Australia, the following crimeswere recorded in 2000:approximately 227,000 residentialburglaries; 139,094 motor vehicle thefts; 15,630 sexual assaults; 9 474 armed robberies; and 342 murders.It is important to realise that thesefigures show recorded crime. Manyminor crimes and some serious crimesare not reported to, or discovered, bythe police.To establish the extent of crime in acommunity, figures are often expressedas rates per 100,000 people. Thisshows that in Australia last year therewere just under 2 murders per 100,000people.It’s interesting to compare Australia’smurder rate with other countries: Brazil 10 per 100,000 USA 7 per 100,000 Everywhere we go, we leave a telltale Switzerland 3 per 100,000 sign of our presence. Japan 1 per 100,000These comparisons may be slightly It is almost The perfect crime?inaccurate because of differences in the There are many examples of unsolvedway crime statistics are collected andused around the world. impossible to and undetected crimes, especially from the past when forensic techniquesEven within a country, different areas be in a place were less sophisticated. Even today,experience different crime rates. there are still crimes committed whereTherefore, figures can give a misleading without the criminal is not discovered.picture of your likelihood of being a More often, however, forensicvictim of crime. What is clear, however, leaving a evidence allows police to link ais that in Australia, violent crime is far suspect to a crime without enoughless common than theft. trace of your certainty to convince a court, and so the suspect is not found guilty. If there presence. are no other suspects connected to the crime, the police must look for more evidence – for example, from later witnesses.Correlation is not proof However, many criminals are unaware of just how readily they canAs in all areas of science, evidence at the scene, may belong to someone be linked to a crime by the skilled usefrom forensic investigation does not else. There are a number of of modern forensic techniques. It ismean proof. A correlation between two possibilities. The suspect may have: almost impossible to be in a placethings does not mean that one causes • committed the murder; without leaving a trace of yourthe other. • been present at the crime, presence in the form of a hair, For example, you might observe that without committing the offence; discarded skin cells, clothing fibresmost people involved in car crashes • been present at the scene or traces of saliva.wear seat belts, but this doesn’t mean innocently or suspiciously beforethat seat belts cause crashes. Your the crime occurred;observation is correct, but you cannot • arrived after the crime and left inuse it as evidence for the cause of fright; or,accidents. You need to make further • been nowhere near the scene andobservations – for example, of people his jacket was used by someonein cars who are not involved in else with or without his knowledge. The author would like to thank thecrashes. Australian Federal Police Forensic Pieces of evidence may not always Therefore, all evidence must be Services, in particular Mr Karl Kent, foragree. A fibre found at a murder scene taken together. Very rarely is one piece generous assistance with this article.may match a male suspect’s jacket, of evidence conclusive proof.but other evidence, such as DNA found