While an extra male chromosome seems like a logical explanation for mutant-aggressive behavior, there is not much evidence that links the X or Y chromosome to serial killers. Testosterone High testosterone in itself is not a dangerous thing, but when it is combined with low levels of serotonin, the results might be deadly. But since not everyone can be the top dog, serotonin keeps the tension from peaking, and mellows us out. When serotonin levels are abnormally low, however, frustration can lead to aggressive, even sadistic behavior, according to a study by Paul Bernhardt. Excess manganese lowers the level of serotonin and dopamine, which contributes to aggressive behavior.
Alcohol increases the effects.
James Huberty, the mass murderer, had excessive amounts of the toxic substance cadmium in his system. According to many researchers, brain defects and injuries have been an important link to violent behavior. The hypothalamus regulates the hormonal system and emotions. Because of the physical closeness of sexual and aggressive centers within the hypothalamus, sexual instinct and violence become connected for lust murderers. The hypothalamus may be damaged through malnutrition or injury.