The murder of Selena was caused by shooting.
 Since most murders are committed by young males, the near simultaneous low in the murder rates of major developed countries circa 1960 can be attributed to low birth rates during the Great Depression and World War II
 Some of the more exotic factors claimed to affect murder rates include the availability of abortion and the likelihood of chronic exposure to lead during childhood (due to the use of leaded paint in houses and tetraethyllead as a gasoline additive in internal combustion engines)

