IN SEPTEMBER, Rockstar Games, a British video games developer, is launching Grand Theft Auto 5, a game in which gamers play a homicidal car-thieving maniac. Fictional crime remains popular. Real criminality, however, is dying out in much of the rich world. In Britain, figures released on July 18th showed that overall crime rates are now as low as they have been since 1981, when the government first started conducting its quarterly crime survey. In America, murder rates are at a forty-year low. What is behind this spectacular improvement? There are lots of theories—and few experts agree. The crack cocaine and heroin epidemics of the 1980s and 1990s have largely burnt out. Electronic crime and fraud has distracted some professional criminals from traditional ways of stealing stuff. Policing has improved, and more people are locked up in prison. The two wildest ideas are the introduction of legal abortion and the phaseout of leaded petrol. Unwanted babies were more likely to grow as criminals, it was argued: that theory is now largely discredited: it doesn’t cross borders and crime has continued to fall long after the effect should have tapered off. Exposure to lead in childhood supposedly creates more impulsive and violent adults. That hypothesis is effective at explaining the reduction in violent crime in the United States but fits less well with other countries; in France, for example, violent crime has increased of late, despite unleaded petrol.

More conventional explanations also fit however. Overall, police officer numbers increased by roughly a fifth between 1995 and 2010. Policing has also got better in many places, with officers using data to work out where to target resources (“CompStat” or “Hotspot” policing) and engaging more with the people on their beat. In the United States, the most improved cities are New York and Los Angeles, which both embraced intensive policing in the 1980s and 1990s. In Detroit, by contrast, where police numbers have been heavily cut, crime has actually increased in recent years. Perhaps the most intriguing idea is simply that many crimes have become harder and less rewarding. The crimes to have fallen furthest and in the most places are property crimes, especially car theft and burglary. Thanks to technology which makes it far harder to hotwire a car—car thieves now have to steal the keys—joyriding has all but died out. Burglar alarms, security locks and so on have had a similar, though less stark, effect on burglary. By contrast in many European countries, robbery increased in the late 1990s and early 2000s as the adoption of mobile phones created tempting new targets.

For the moment, few people agree on the relative significance of all of these factors. All or none may have contributed to the fall in crime, in different quantities in different countries. For criminologists and other social scientists, trying to assess the causes is a growth industry. For the rest of us, we can at least play Grand Theft Auto without fear of being mugged on the way back from the shop.