Category Science

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’.

Picture Credit : Google

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.

Picture Credit : Google

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.

Picture Credit : Google

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.

Picture Credit : Google

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.

Picture Credit : Google

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.

Picture Credit : Google