By Jonathan Amos
BBC News science reporter, Norwich
UK scientists say their new system for checking fingerprints is having a big impact in the fight against crime.
Manual fingerprinting takes time
Six police forces are now using the technology, which relies on new compression techniques to transmit digital prints over mobile phones.
Professor Nigel Allinson from Sheffield University said matches could now be made within hours as opposed to days.
The time saved has allowed police to arrest known burglars earlier, reducing the incidence of crime.
"Where this system was first trialled in Lincolnshire, burglaries dropped by 40%," the researcher told the British Association's Science Festival.
"This is because if you catch someone after a day rather than two weeks, it makes all the difference; it's usually only a small number of people who commit house burglaries."
Ridge and furrow
The system equips scenes of crime officers with a digital scanner and a laptop with a wireless card.
The investigators will make physical copies of prints in the traditional way, but instead of waiting until perhaps the end of the day to return them to the lab, the officers can also now return electronic copies immediately for cross-checking with criminal records.
This has been made possible by a process of 15-to-one compression which allows the file to be transmitted in under a minute but still retain sufficient detail to make a match possible.
"Limited bandwidth means that a normal fingerprint image would take between four and 20 minutes to transmit, which is far too long. So you have to compress the image, and in doing that you can lose information," explained Professor Allinson.
"Fingerprint identification is all about looking for minutiae - for discontinuities in the ridge and furrow pattern. Experimentation has determined the optimum level of compression which allows officers to transmit prints with no loss of information in 30-60 seconds."
Once an image is back at the lab, it can be checked against computer records in the normal way. The fastest time from dusting a print to making a match is just two hours.
The rapid print checking system is now being rolled out to all 43 police forces in England and Wales after being approved by the National Fingerprint Board earlier this year.
Professor Allinson's team is also developing a system to electronically cross-match shoeprints left at crime scenes.
New powers under the Serious and Organised Crime Act oblige suspects to give impressions of their footwear, and permit police to store this evidence on a searchable database.
The computer system being developed by the Sheffield team would allow for rapid comparison of those sole impressions with 12,000 known models of shoe.
The technology will have to be robust enough to cope with different sized shoes and partial prints.
Such evidence does not have the unique qualities of DNA or fingerprint evidence, which can tie evidence to a particular individual; but police are convinced shoes can give them valuable leads, especially when footmarks may be the only trace a criminal leaves at the scene.
"The West Yorkshire force, for example, examines 10,000 crime scenes annually," said Professor Allinison. "Forensic scientific support is important both for volume as well as serious crime. There is a recognition that we need to make scientific support more effective and efficient, and to take a more proactive role."