Category Techniques

Genetic fingerprinting has changed the course of crime detection. It is the most accurate method yet developed of identifying individuals. The probability against any two genetic fingerprints being the same by pure chance is greater than the number of people on Earth. The technique can also prove paternity of children and is being used to control the breeding of rare animals.

Professor Alec Jeffreys, a British geneticist at Leicester University, discovered genetic fingerprinting in 1984. He was conducting research into DNA – the chemical substance in the nucleus of every living cell which determines a person’s individual characteristics, such as the colour of hair and eyes. The structure of DNA is different in everybody, with the exception of identical twins.

Professor Jeffreys discovered that within the DNA molecule there is a sequence of genetic information which is repeated many times along the structure of the DNA, which looks like an endless twisting ladder.

The length of the sequence, the number of times it is repeated and its precise location within the DNA chain are unique to each individual. A process was developed to translate these sequences into a visual record. The finished picture, the genetic fingerprint, is a series of bars on an X-ray film, rather like the bar codes printed on food packets.

To obtain a DNA specimen, a scientist only needs a biological sample containing some human cells. This is usually blood, semen or hair, and only very small amounts are necessary.

Genetic fingerprinting is an important in establishing innocence as guilt. For example, a burglar who breaks a window may leave a blood sample behind on the glass. This can be used to create a genetic fingerprint. When police arrest a suspect, a blood sample can be taken from him and compared. If it matches, he is the burglar. If it does not, he is innocent.

When the police have a genetic fingerprint, but no suspect, they can fingerprint groups of people by taking samples of their blood. The first mass genetic fingerprinting happened in Leicestershire in 1987 when samples were taken from 5500 men living around a village where two young girls had been raped and murdered.

The killer was eventually found when a man was heard to say that a workmate had asked him to take his place when the samples were being taken. Another man who had previously been accused of one of the murders was freed because his genetic fingerprint did not match those made from the scene-of-crime evidence.

Genetic fingerprinting can also determine who is the father of a child and resolve paternity disputes. A DNA strand is made up equally of the characteristics of each parent. By comparing the genetic fingerprints of mother and child, a scientist can say with certainty that the parts of the child’s fingerprint which do not match those of the mother must have come from its true father.

Another use is in bone-marrow transplants which are given to people suffering from leukaemia. Doctors can check whether the genetic fingerprint extracted from a patient after a transplant matches that of the donor. If it does, the transplant has been successful and is producing healthy white blood cells. If it does not, the transplant has failed to take. This allows the possibility of another transplant.

Zoologists can use genetic fingerprinting to control the breeding of rare animals and preserve species. They can compare genetic fingerprints taken from animals to ensure that inbreeding among endangered species, which is known to lead to weaker animals, is avoided.

 

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Fingerprint evidence led to probably the only case in which two brothers, jointly convicted of murder, were executed by two other brothers.

In 1905, Alfred and Albert Stratton were accused of murdering an elderly couple who were battered to death above their shop in London.

Lying on the floor next to the bodies was an emptied cashbox in which the couple had kept their takings. On the box’s metal tray, fingerprint officers found the impression of a sweaty or oily thumbprint which did not match those of the dead couple – or that of the first police officer at the scene.

Suspicion fell upon the Strattons, both known housebreakers. They were arrested and tried at the Old Bailey. The thumbprint was the main piece of evidence.

Bothe men were found guilty and sentenced to death. They were hanged together by the brothers John William Billington, the public executioners, on May 23, 1905.

‘Mr Fingerprints’

The comparison of fingerprints for catching criminals was first developed in the 1890s by Edward Henry, the British inspector-general of the Indian police in Bengal.

Previously, the usual method of registering the characteristics of criminals was the anthropometric system, developed by Alphonse Bertillon, a French criminologist. It involved measuring the criminal’s arms and legs, and taking photographs from the front and sides.

Edward Henry became interested in fingerprints which had previously been used to study racial characteristics and evolution. He instructed his police officers to take impressions of criminals’ left thumbs in the belief that as most people were right-handed the ridges on the left thumb would be less worn. He then went on to devise a system based on the patterns of prints which was adopted in India.

His revolutionary ideas attracted interest in England, and in 1901 he was put in charge of the Criminal Investigation Department at Scotland Yard. He set up the first Fingerprint Branch which made more than 100 successful identifications within six months.

Henry later became Commissioner of the Metropolitan Police. He retired and was made a baronet in 1918, but was always known as ‘Mr Fingerprints’.

 

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The matching of fingerprints requires good eyesight and intense concentration.

The process is similar to one of those puzzles where you have to spot the differences between two apparently identical pictures. With fingerprint identification, the reverse applies – the fingerprint expert has to look for the similarities.

Fingerprints are normally stored by name on card-index systems at a control fingerprint bureau. In most countries, only the prints of convicted criminals together with unidentified marks in unsolved cases are kept.

Some countries keep a national archive of fingerprints but because of the time it can take to search, it is usually considered as only a back-up, for use if a mark is not matched locally.

Files of criminals with known specialties, such as car thieves or handbag snatchers, are also kept. Secret police forces and intelligence organizations also keep their own files of people they consider to be revolutionaries or enemy agents.

A fingerprint officer will begin by examining the marks taken from the scene and memorising their characteristics. He will then compare them against prints taken from innocent people who might have left marks at the scene – members of the family or policemen, for example. Any marks that match the innocent prints are rejected. The fingerprint officer then takes from the file all prints of possible suspects, whose names have been supplied by the investigating detective.

If these do not match, the officer has to make a wider and more painstaking search. If he is searching for a burglar, he will begin looking through all burglary cases in the locality and then all those from the adjoining town or area.

Depending on how much time was ordered to be spent on the search, he might pursue it through neighboring fingerprint bureaus in other police forces. The search for a house burglar can be widened to other potential types of criminals, such as safe-crackers, but the officer might not feel it worthwhile to extend the search to criminals who only pass bogus cheques.

Fingerprint officers also check the fingerprints of newly arrested criminals against unidentified marks from other crimes in the hope of clearing up unsolved cases. They will also compare unidentified marks against new marks to see if a series of crimes can be established. Officers can make dozens of comparisons a day, but many work for days without ever having a positive identification.

Most of this work is manual and can be very laborious. In the early 1980s electronic systems were developed to speed up the work. Prints and marks can now be stored and retrieved on electronic indexing systems, so that the press of a button calls up all the prints of, say, known car thieves living in a certain area and aged under 30. Systems can now be linked up between neighbouring forces, or with national collections, to widen the potential search. However, the actual comparison still has to be carried out by the fingerprint officer.

Scientists around the world are developing computer systems which store, retrieve and, most importantly, match prints and marks. Some matching methods, which can make 60,000 comparisons a second, are already being used by local police forces. But a fully automated, national fingerprint system is still in the future.

 

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Gloves yield distinct prints in much the same way as human flesh because of the grease which accumulates on the surface. Glove prints can also be revealed by a layer of powder and if they can be matched with a glove found in the possession of a suspect, it becomes powerful evidence.

The prints can distinguish the type of leather or fabric, its age, and the type of stitching used.

The first case of its type in the world was in 1971 at the Inner London Quarter Sessions. Police had obtained a print from a left-hand glove a burglar was believed to have worn while breaking a window. The print matched that of a pair of sheepskin leather gloves found in the possession of the suspect. He pleaded guilty.

 

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The traces, actually called fingermarks, consist of tiny amounts of moisture which form patterns corresponding to the ridges and lines on the fingers and other parts of the hand. Non-absorbent materials such as plastics and painted surfaces produce better marks than absorbent ones like fabrics. Marks are normally invisible unless they have been left by paint or blood. So a police fingerprint expert coats likely surfaces with very fine dust, often powered aluminium. The particles stick to the moisture traces, making them visible. Sticky tape is then places on the mark to lift away an impression of the pattern, which can be taken away and photographed. Some fingermarks are now photographed on site.

Modern technology is now helping the police to obtain marks from some previously bags and smooth leather.

One method called vacuum metallization involves putting the surface into a container from which the air is expelled, creating a vacuum. A layer of gold, then a layer of zinc, is evaporated onto the surface. The gold is deposited uniformly over the area, but it is absorbed by the ridges of moisture which make up the fingermark pattern. Zinc will only condense onto another metal, so it adheres to the gold-coated areas, enhancing them to provide a contrast with the uncoated fingermarks. The pattern of marks is then photographed.

Once the photograph is obtained, it is compared with fingerprints of known criminals held on police files. There are four main types of fingerprint pattern. The patterns are divided up into such features as ‘forks’, ‘lakes’, ‘spurs’ and ‘islands’.

For an identification to be presented in court, a number of recognizable features of the mark of a single finger or thumb must correspond with the same number of features on the print. The number varies between countries, but can be as high as 17. If the mark shows more than one finger the court will usually accept fewer features per finger. Most fingerprint officers and detectives regard more than eight features as enough to confirm identity. Although this would not be presented in court, it would be enough to concentrate investigation on a suspect.

 

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Gloves yield distinct prints in much the same way as human flesh because of the grease which accumulates on the surface. Glove prints can also be revealed by a layer of powder and if they can be matched with a glove found in the possession of a suspect, it becomes powerful evidence.

The prints can distinguish the type of leather or fabric, its age, and the type of stitching used.

The first case of its type in the world was in 1971 at the Inner London Quarter Sessions. Police had obtained a print from a left-hand glove a burglar was believed to have worn while breaking a window. The print matched that of a pair of sheepskin leather gloves found in the possession of the suspect. He pleaded guilty.

 

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An X-ray – as used on the Millet picture – is the most common method of uncovering hidden paintings. Long wavelength X-rays are used because they are easily absorbed by paint. The degree of absorption depends on the type of paint. For instance, lead and cadmium-based paints are more absorbent than those containing chromium or cobalt. Thicker layers of paint will absorb more than thinner ones.

Photographic film is placed behind a suspect painting, and X-rays are passed through it from the front. When the film is developed, the ghostly outlines of earlier pictures may be seen.

In the early 1980s, for instance, two art restorers in Glasgow – both of them superintendents radiographers in a local hospital – X-rayed Rembrandt’s Man in Armour. They discovered what appeared to be a white plume blowing in the wrong direction from the top of the helmet. However, on turning the X-ray picture around, the ‘plume’ was seen to be part of an abandoned work by Rembrandt: a lady in a flowing white dress and headdress. Man in Armour is in the Glasgow Art Gallery and Museum.

Similarly, a painting by the 16th century Italian painter Paris Bordone – Saints Jerome and Antony Abbot commending a Donor – was found after X-ray to have two donors, one of them by an unknown artist. The painting is also in the Glasgow gallery.

X-rays are also used to study pentimento, the changes an artist makes while producing a painting. Alterations to the compositing, changes in the angle of an arm or a head, will all show up under X-ray, and are useful to art historians and restorers. (The word pentimento comes from the Italian word pentersi, ‘to repent’, suggesting a change of mind by the artist.)

Charcoal outlines

Infrared light is also used to discover paintings beneath paintings. When infrared light is shone on the picture it penetrates the surface paint and it reflected. The reflection is recorded on a camera. The effect is to make the thin, upper paint levels transparent, so revealing the charcoal outlines of the artist’s preliminary drawing. The technique has been used by New York’s Metropolitan Museum to study Flemish Renaissance paintings.

In some cases it reveals details not apparent on the final painting, and helps in understanding the artist’s technique.

 

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When Jean Francois Millet’s dramatic picture The Captivity of the Jews in Babylon was unveiled in the late 1840s it was vilified by public and critics alike.

The Paris critics thought the picture’s surface was too heavily encrusted with paint, and at least one of them complained about the undue savagery of the scene. ‘The soldiers are pressing the Jewish women… with more violence than is necessary,’ he wrote. ‘They behave as if they were attacking or sacking a city.’

The picture then vanished from sight and art experts assumed that Millet had destroyed it. In the winter of 1983, however, art restorers at the Museums of Fine Arts in Boston, Massachusetts, used X-ray radiography to reveal the presence of another picture under the surface of Millet’s portrait The Young Shepherdess.

The X-ray picture showed the image of Millet’s ‘long lost’ and controversial Captivity. It is now assumed that, far from destroying the picture, Millet reused the canvas more than 20 years later when art materials were in short supply during the Franco-Prussian War of 1870-1.

 

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On New Year’s Eve, 1986, one of the most disastrous fires since the Second World War killed 97 people in a hotel in Puerto Rico. Workers at the hotel, the Dupont Plaza in San Juan, had become angry over the lack of a pay settlement, and two of them used methylated spirit to set fire to cardboard boxes and other rubbish in an empty ballroom.

Within 15 minutes the flames had engulfed the entire ground floor and trapped hotel guests on the top floor of the 21-storey building. Many of the 1400 occupants had to be rescued by helicopter. As well as the 97 dead, there were 140 people injured.

Investigators from the US Bureau of Alcohol, Tobacco and Firearms were on the scene while the fire was still raging. When they examined the charred remains of the furniture in the ballroom later, they discovered traces of the methylated, spirit and decided that the fire had been brought in to interview hotel staff.

Eventually, three employees were arrested – one charged with lighting the fire, one with assisting him, and the third with supplying the spirit. All three were convicted and given prison terms ranging from 75 to 99 years.

Fire investigators are among the first on the scene after a fire has been put out. Their first task is to preserve and record the remains. Sometimes it is clear that an arsonist has been at work: fires may have been started at several points, or someone might have been spotted running from the scene just before flames were noticed.

The next task is to locate the place or places where it was most intense. The spread of the fire must also be tracked. Much can be learned by looking at smoke patterns and damage to surfaces. Metals and glass can be useful guides. A metal rail will distort or melt according to its proximity to the hottest part of the fire. The density of cracks in glass usually corresponds to the intensity of heat.

Expansion of metals can also be revealing – a steel joist 33ft (10m) long and heated to 932  (500  will expand by 2 ¾ in (70mm). the depth of charring in wood or in layers of carpet also gives an indication of the heat or duration of a fire.

Against this must be balanced factors which help to spread fire. Lift shafts, air vents and stairwells give a chimney effect, raising hot gases to other parts of a building and creating secondary seats of fire. The investigator can be confused by localized fires caused by broken gas pipes or stored fuel. Exploding aerosol cans can create fireballs several feet across.

Having found the seat of the fire, the investigator will look for signs of the cause – empty petrol can leave by an arsonist, charred wiring that indicates a faulty electrical connection, even a fragment of carelessly discarded match.

Forensic scientists are skilled at examining fragments of burnt materials. After one of Italy’s worst fire disasters, the burning of the Statuto Cinema in Turin on February 12, 1983, in which 64 young people died, the projectionist was able to point to the site where the flames first appeared. Fire inspectors discovered the remains of old wiring which had started the blaze.

When remains of the wallpaper, carpeting and upholstery were sent for forensic examination in Rome, scientists found that contrary to Italian fire safety regulations none of these had been fireproofed. After a lengthy trail, the cinema owner, the supervisor of the redecoration work and two local fire officers, who had declared the cinema to be safe, were all sent to prison for between four and eight years.

If no cause of a fire is apparent the investigator might find that a dead body was a murder victim, suggesting the fire was started to cover up the crime. A human body is extremely difficult to burn away completely and the remains can tell investigators a great deal. There could be more intense burning of the body than its surroundings, suggesting that it had been set alight first, or evidence of asphyxiation in the remaining lung tissue, indicating that the person had been strangled.

The fire which killed 31 people at King’s Cross Underground Station in London in November 1987 was first believed by some to be arson. It began on an escalator and was fanned by the draught of air coming from the train tunnels below ground. Investigators finally concluded that it began in accumulated fluff and grease under the escalator, almost certainly ignited by a discarded match. Smoking had been banned on underground trains in July 1984, but many people lit cigarettes on the escalator as they were making their way out of the station.

 

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The lie detector is an assembly of three different instruments. Their outputs are fed separately to the lie detector and recorded as separate traces on a graph.

One instrument, the pneumogram, records breathing patterns. A rubber tube is strapped across the chest, and instruments measure fluctuations in the volume of air inside the tube, which are brought about by variations in breathing.

The second instrument, the cardiosphygnometer, detects variations in the blood pressure and pulse rate. The information is picked up by a bladder and cuff placed over the upper arm, in the way that doctors check blood pressure.

The third instrument is the galvanometer, which monitors the flow of a tiny electric current through the skin. The skin conducts electricity better when it is moist with perspiration. Electrodes are usually taped to the hand.

 

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