Dusting down

As the office manager for the Eastern Unit, Jon manages a crack team of 20 investigators who are responsible for gathering crucial evidence where any sort of crime has been committed in the area, often utilising clues which are so small they are invisible to the naked eye.

Indeed, what might seem pretty insignificant to you or I - a cigarette butt perhaps, or a few fibres of material - could mean a life sentence for the crook who inadvertently left them behind.

"Every contact leaves a trace," explained Jon. "We're looking for evidence of these points of contact, such as shoe prints, fibres and fingerprints."

In fact, fingerprints were once the best weapon in the armoury of a crime scene investigator - until the introduction of DNA profiling.

Cellular material such as saliva, blood and semen all contain DNA - or deoxyribonucleic acid - the profile of which is unique to the individual.

As recently as the early 1990s a blood stain the size of a 10p piece was needed to get a successful result. These days, a DNA profile can be obtained from a microscopic sample.

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And thanks to phenomenal advancements in forensic technology, a full DNA profile can produce results with an accuracy of one in a hundred million.

"We used to only use blood grouping techniques which gave statistical results in the region of one in 50, but now the DNA profiling techniques are much more discriminatory," said Jon.

"The Crime Scene Investigation Unit is impartial, but we want to make sure the right offenders are punished for the crime.

"People often think the system is on the side of the criminal, as they have certain rights, but with such a high success rate in DNA profiling the balance is being redressed. More offenders are being brought to justice yet our results may also help to disprove the involvement of an individual suspected of committing crime."

The advancements in the system even mean that unsolved cases from tens of years ago are being reopened, and people are being convicted on evidence which at the time could not be properly investigated: a sobering thought for the criminals of yesteryear.

As forensic technology has grown, so has a national database containing DNA and fingerprints of convicted criminals. It means that even if someone who lived in Yorkshire left fingerprints or DNA while committing a crime in Dorset, they would still get caught.

"From April this year, we have the powers to take DNA and fingerprints from people who are suspected to have committed a recordable offence - and we can now do this upon arrest and not charge. These stay on the database even if the person is acquitted."

Yet there are plenty of other things that can point to a criminal. Even the likes of shoe prints are recorded.

"These days, the role involves intelligence as well as evidence gathering," explained Jon. "You have to look at the bigger picture.

"One pair of shoes, for example, put someone in prison for seven years. They belonged to a burglar who decided to scour a notch out of the soles of every time he committed an offence to make them look different. Actually, it just made them stand out even more!"

Similarly, one blundering burglar decided to burn his own fingerprints with acid - in the event they were easier to identify as they were so unique.

Jon's team of crime scene investigators (formerly known as scene of crime officers, or "socos") is based in Ferndown, but covers half of the county including Poole, Bournemouth and Christchurch, as well as an area encompassing Blandford in the west and Gillingham to the north.

The majority are civilian police staff, usually with a background in photography, employed by Dorset Police. Jon believes it takes five years to become fully proficient in the role.

"We have found incriminating fingerprints underneath toilet seats, for example," said Jon. "Some burglars forget about things like this and automatically take their gloves off before having a wee.

"We also caught another criminal who kept re-visiting a particular house. One day he just got blas and forgot to put his gloves on. We found his prints all over a jewellery box."

On another occasion someone broke into County Hall, and the thirsty con man stole a can of drink. Little did he know he left DNA evidence via saliva on the can.

"In some shape or form, a criminal will always leave traces of themselves at the scene of a crime - or take traces of the crime scene away with them - and in an age where forensic science is moving forward in leaps and bounds, I think the perfect crime just doesn't exist any more."

FINGERPRINTS

Caused simply as a result of sweat on the fingertips, fingerprints are the classic examples of forensic evidence.

No two are alike - even if they belong to identical twins. However, this is of limited value to an investigating officer. They are more concerned about whether a print on their files exactly matches a print found at the scene of a crime or a print of a suspect.

It took the research of William Herschel (1833 - 1917); Henry Faulds (1843 - 1930) and Francis Galton (1822 - 1911) to show, over many years, that no two individual's prints exactly matched one another. And it needed the classification system designed by Edward Henry (1859 - 1931) to establish a means whereby one print could be quickly compared with many thousands held on file.

Fingerprints are formed from minute ridges of hard skin, quite different in character from normal skin. Known as friction ridges, they loop and swirl on the fingertips in the clearly defined patterns described in the Henry system: arches, loops and whorls.

A fingerprint can last forever in the right environment, but often has to be enhanced with chemicals or a dusting of powder in order for it to be photographed effectively.

Aluminium is a general all-purpose powder but black, white and fluorescent is also used. An appropriate choice of powder is crucial to the successful enhancement of a fingerprint.

The surface material on which the print is found also plays a factor in its enhancement. So involved are the different processes, CSIs often refer to a thick manual listing the various chemicals and treatments.

One substance often used to enhance fingerprints is Superglue. It will fluoresce under an appropriate light source.

WHAT HAPPENS AT THE SCENE

Crime scene investigation involves three core areas: photography, forensics and fingerprints. The principles are the same at every scene, whatever the crime.

In the case of a murder, drawing a line around the body is a myth. No member of Dorset's Crime Scene Investigation Unit has ever done it or seen it happen.

In the case of a burglary, a uniformed police officer is first person to go to the scene. A crime scene investigator will be considered to attend every burglary scene. They are on duty between 8am and 10pm but are on call out of office hours.

Appropriate clothing is worn (including overalls, masks and gloves) so the area is not contaminated.

A "risk assessment" is carried out to identify the best sequential process of gathering clues, and all consequences of any actions are considered. Every opportunity to gather evidence is maximised.

In light of the above, decisions have to be made. For example, if a fingerprint in blood is found at a crime scene, taking a sample of the blood would destroy the print. A photograph must be taken to keep a permanent record. Only then can the blood sample be taken.

A computerised record of all forensic examinations is generated which is unique to that particular crime scene.

The victim is interviewed to establish exactly what they know about the incident.

A visual examination is carried out to formulate an explanation of events. In the case of a burglary, this would include looking at how the person gained entry. Is there any evidence on a fence or a window - or footprints in the soil? Did the offender gain access through a neighbour's garden? Were security lights tampered with?

The least destructive examination needs to be done first, and a CSI is careful not to touch anything. The public is asked to disturb the scene as little as possible in case they inadvertently destroy evidence or even introduce extra evidence.

If evidence is found on a removable item, the CSI will recover it, but if a fingerprint is found on a wall, for example, it will be dealt with at the scene.