Smart cameras will spot the guilty before they commit a crime

They record our every move from almost every vantage point. But soon CCTV cameras will have another power: the ability to predict crime on Britain's streets.

Researchers at Sussex University have discovered how CCTV camera controllers spot criminals by studying the way they walk.

The team of psychologists studied 10,000 excerpts from CCTV footage and found a number of 'trigger signals' in criminal behaviour which showed when offenders were about to commit a crime.

The footage showed how car thieves tended to walk erratically and look in directions irrelevant to their path of travel. Before an act of violence culprits would walk aggressively, their arms static by their sides, taking long purposeful strides.

Professor Tom Troscianko of the School of Cognitive and Computer Sciences, who headed the study, said researchers chose a hundred scenes from CCTV footage filmed around the country. Each scene lasted 15 seconds and they were based around three scenarios: a fight outside a public venue, violence against property in the street, and car theft in an underground car park. Some scenes depicted the moments prior to a crime while others showed activity that did not result in a crime.

A hundred people - 50 professional CCTV controllers and 50 civilian volunteers - were asked to watch the footage and guess which scene would result in a crime and indicate when during the 15 seconds they had reached their decision.

'The actual crime was never shown' said Troscianko. 'In each sequence we recorded the exact movements of the people. We looked at the moments in each sequence which increased the chance of people making the right prediction that a crime would happen.'

The types of behaviour were then ranked. 'When these trigger factors were present, like a type of walk or a type of "gaze behaviour", we saw that people were approximately twice as likely to predict a crime' said Troscianko.

Before a violent act like a fight, an assailant walked in a very aggressive way. 'The stride length and speed of walk would increase, but they would not run. Their arms did not move much, and tended to stay down at their sides. They walk in a direct line purposefully.' Similar patterns were observed before damage was done to property.

Before a car theft a culprit would walk slowly or even remain still while looking around. 'He will be looking to see if he is being observed.'

The team are now seeking funding to develop software to continue their work. But campaigners have expressed concern at a new breed of 'intelligent cameras' raising concerns of a Big Brother society.

MP Simon Hughes, the Liberal Democrats' home affairs spokesman said: 'CCTV needs to be used as the exception and not the rule in public places and only rarely in private places.'