This raised the question: was Rifkin's killing spree somehow triggered by traumatic events like his father's suicide, or his own experience of being bullied? Dr. Peter Breggin, with the international center for the Study of Psychiatry, thinks constant humiliation or abuse can actually lead to violence, claiming most people who commit murder don't feel strong, but feel weak. .
Dr. Craig Ferris, from the University of Massachusetts, tried to prove the link between violence and past abuse by studying hamsters. Hamsters exhibit aggressive behavior but never physically harm one another. Ferris performed a social experiment on the animals that he could never have performed on humans, manipulating their environment, to see exactly how abuse might affect aggression. He placed an adolescent hamster in an abusive situation: the home cage of an older, bigger hamster. The larger, more aggressive hamster chased and threatened the smaller one. As an adult, the abused hamster became more afraid of hamsters that were the same size or larger while becoming more aggressive, and ruthlessly attacking smaller, weaker hamsters. This change in behavior is fueled in part by a change in biology: when the hamster's brain becomes sensitive to vasopressin, it tells the body to fight, while at the same time, becoming numb to serotonin, the brain's peacemaker. .
Dr. Anthony Bolton, a brain specialist, conducted the first series of neuropsychological tests on Rifkin in 1994. Surprisingly, Rifkin performed very well on most of the tests. One test, however, showed signs of dysfunction: He was to place his hands palms down on the table, raise his index finger when the test administrator knocked on the table once, and do nothing when he heard two knocks. Out of 100 tries, most people make a mistake only once or twice; Rifkin failed sixteen times. Bolton claimed Rifkin had difficulty controlling his movements and his behavior.