A new theory of crime: Driven down IN 1997 DMA Design, a British developer, launched the first version of "Grand Theft Auto," an enormously successful video game in which players routinely steal cars. They would be unlikely to come up with the idea now. In 1997 some 369,000 vehicles were stolen in Britain; last year the number was just 94,000. That much is familiar. But Graham Farrell, a criminologist at Loughborough University, believes the drop in car theft helps to explain why overall crime rates have fallen since the mid-1990s - and not just in Britain. Car theft, he argues, is an opportunistic "debut crime" which can start a criminal career. Those who steal cars for fun often go on to become burglars or muggers. And Mr Farrell points out that a stolen getaway car is often necessary to commit serious crimes such as armed robbery. Technology that makes it harder to steal a car, such as vehicle immobilisers and central locking, thus reduces the number of career criminals. It is just one of many competing explanations for the decline in crime in rich countries that began in the 1990s. But Mr Farrell's has the advantage of crossing borders. It may explain, for example, why crime started falling later in Canada than in America: immobilisers were not mandated in Canada until 2007. That some other crimes have risen, such as mobile phone theft and internet fraud, supports the idea that a lot of criminal activity is opportunistic. And it makes intuitive sense too: as players of "Grand Theft Auto" know, it is hard to get anything done without a car.