Soles can be incriminating. Pic: Forensic Science Service 2007
How much can you tell about a criminal from their shoeprints? A lot, it seems, which is why Britain is launching the world's first online collection of prints. But could any of us be nicked for wearing the same shoes as a bank robber?
You would think that the impressions you are leaving behind with your Reeboks, Nikes, Converse All Stars, whatever, are nothing special. Those kind of shoes come rolling off the production line in their thousands every day, don't they?
But the brand you are wearing, the scuffs and damage your shoes have suffered, and the way you have worn them down in particular places, make that print identifiable as yours and can place you at the scene of a crime, say experts.
That's why for years detectives have sought footwear imprints - the second most common evidence type left at crime scenes - that can be analysed against the shoe of a suspect. Under new laws those prints can be taken from suspects who pass through custody, even if they have not been charged.
But until now much of that information has been on paper only and has not been effectively shared nationwide.
With the launch by the Forensic Science Service of its new Footwear Intelligence Techology (FIT) system the data will be accessible to all police forces online.
One part will contain about 13,000 images of the shoe print types most commonly found at crime scenes - lots of training shoes but not many stilettos - which officers can use as an online reference library to match it to the type they have found.
Secondly, police can enter footwear prints and other details from the particular crime scene they are investigating, to help with the linking of different offences by the same person.
Manager of the Forensic Science Service's (FSS) footwear section is Jonathan Goodyear, who has been in the shoe print science game for 20 years.
"Many criminals will commit different burglaries, for example, wearing the same shoes. They might have a specific pair of shoes they burgle in."
Peter Voisey, 35, was convicted in 2006 of abducting a six-year-old girl from her bath and raping her.
In the days following the abduction, detectives struggled to win support for their theory that the crime had been an opportunistic one.
Among the evidence brought to court was a footprint recovered from the bathroom by forensic investigators, which matched a pair of trainers Voisey owned.
"We may have 10 scenes with the same footprint, but that does not tell us who the offender is. But if at one of those scenes there is a fingerprint, or DNA has been left behind, that would give us a name."
"It is an intelligence tool to actually link crimes together," he says, adding that although it could be used alone it is more often useful as supporting evidence.
Such evidence helped convict "a well organised and ruthless gang" in December 2006, says the FSS.
Police in four English forces worked with forensics experts on investigating a series of aggravated burglaries in which premises were being ram-raided and armed robberies being committed.
The recovery of 25 footwear marks helped link different scenes across the counties and also connected a number of the suspects with the crime scenes. Seven men were convicted and six of them jailed for a total of 74 years.
After the imprint is collected by a crime scene investigator a forensic process is followed, looking at the pattern, size, wear and damage features. Investigators can even detect prints invisible to the naked eye by using similar methods to those employed to discover fingerprints - such as using powder and special lighting.
But it's not straightforward, concedes Mr Goodyear. Not least because the print from a particular shoe can change over time.
But aren't many shoes the same?
"That's why examination of prints at crime scenes against someone's shoe is a complex subject, because there are so many factors. A fingerprint won't change, but a shoe can.
"What you need are enough features, such as damage features, to satisfy a scientist."
Civil liberty campaigners have long objected to the taking and holding of data beyond the immediate aim of detecting crime, saying they have concerns over how such information is held and potentially used by other agencies. But the FSS' footwear team say the arguments deployed against ID cards do not apply to this new database.
"What we have is on the one hand a reference collection of shoe types, it's not every single person's shoe print. For the scene of crime and suspect database we would enter data from people's actual shoes," adds Mr Goodyear.
"It is not a national database in the way we have one for DNA."
"And it is up to individual forces if they want to use the system."
Footprints can be found in all sorts of places
And what if an innocent person happens to have a similar shoe to a serial burglar?
"FIT is not something that is to be put before a jury, it is a place to store data about crime scenes. To get that evidence we would need to seize the shoe, do a detailed examination of it, comparing it with the crime scene mark, and then present that evidence to the court.
"That examination would be done by a forensic expert."
But no system that relies on expert analysis is perfect.
Just one example was the freeing from prison in 2004 of a man convicted of murder on the basis of his earprint.
Experts claimed Mark Dallagher had left his unique earprint on the window of the victim's house, but later a DNA profile obtained from the print proved that it was not his.
One of his lawyers James Sturman, QC, was quoted as saying the case was an example of "the dangers of police following science too closely".