Part of the answer was quite simple, Richard Rosenfeld, a member of the US national consortium on violence research, told the meeting.
First of all fewer people were getting married so there were fewer spouses to murder. The increased status of women and the influence of domestic violence services had also encouraged the drop in spousal homicide.
Secondly, the dramatic rise of numbers in prison had removed more potential killers from the homicide arena.
From 1980 to the mid-1990s the rate of imprisonment in the US had tripled. At least one fourth of the decline in homicides could be explained by the fact that inmates were likely to be drawn from the most dangerous neighbourhoods.
"That must be counted as good news, but it comes with a huge price tag," he said. He calculated that to avert one homicide, there had to be a net increase of 670 prisoners a year.
However, these two factors could not explain all of the drop in killings. "More prisons and fewer families are at best temporary, limited and negative remedies for violence."
There was a third factor. "What we may be seeing is a real and sustained intolerance for unregulated violence. Historians call it a civilising process," he said.
