Varför var det så mycket seriemördare mellan 1970 till 1990-talet?

Proponents of the lead–crime hypothesis argue that the removal of lead additives from motor fuel, and the consequent decline in children's lead exposure, explains the fall in crime rates in the United States beginning in the 1990s.[17] This hypothesis also offers an explanation of the earlier rise in crime in the preceding decades as the result of increased lead exposure throughout the mid-20th century.[18]

The lead–crime hypothesis is the proposed link between elevated blood lead levels in children and increased rates of crime, delinquency, and recidivism later in life.[1][2][3][4]

Lead is widely understood to be highly toxic to multiple organs of the body,[5] particularly the brain.[6][7][8] Individuals exposed to lead at young ages may be more vulnerable to learning disabilities,[9][10] decreased I.Q.,[11] attention deficit hyperactivity disorder,[12][13] and problems with impulse control,[14] all of which may be negatively impacting decision making and leading to the commission of more crimes as these children reach adulthood, especially violent crimes.[15]

The F.B.I. believes that less than one per cent of the killings each year are carried out by serial killers, but Hargrove thinks that the percentage is higher, and that there are probably around two thousand serial killers at large in the U.S.