While a person may never have killed before, it’s likely that he or she already was afflicted with a hidden genetic predisposition and/or psychological trauma, ticking time bombs that were waiting for the right amount of stress to set them off.
“Typically, with people who haven’t engaged in violent acts previously, you see a family history of violence,” Dr. Lipman says. “And there’s also some dramatic trigger, an event that causes the person to feel extreme hopeless and rage, of the sort that’s expressed in a suicidal and homicidal act.”
Based on the information that has emerged so far about DiMaggio, Dr. Lipman sees him as a textbook example. DiMaggio’s father, a chronic drug abuser with a history of violence, reportedly also became obsessed with a teenage girl in the late 1980s.
When she rebuffed his advances, the older man invaded her home with a shotgun and handcuffs and attempted to kidnap her. ("I asked him not to kill us, and he said, don't worry you won't feel a thing,” the victim, who now is an adult, told San Diego TV station KFMB.) But the abduction failed, and the elder DiMaggio eventually committed suicide in 1998.
That disturbing family history -- and DiMaggio’s eventual reenactment of his father’s behavior -- lead Dr. Lipman to suspect that the elder DiMaggio may have passed along to the son a genetic tendency for antisocial personality disorder. Individuals with the disorder can seem charming and likable, but that only masks their capacity to engage in impulsive violence with no remorse or regard for others, according to an article on the Mayo Clinic website.
“It’s usually passed from male to male,” Dr. Lipman explains. “It’s likely that the son was carrying that genetic propensity.”
Dr. Lipman also notes that DiMaggio and his siblings were sufficiently worried about inheriting their father’s violent personality that they swore a pact not to emulate his behavior. It was a promise that DiMaggio ultimately failed to keep, when he found himself in danger of losing his home, and began experiencing feelings of attraction toward the teenage girl that he drove to gymnastics meets.
“When a person has the underlying tendency for the disorder, and then something goes terribly wrong in his life, he experiences feelings of hopelessness and rage that can cause him to become violent and suicidal, even though those things haven’t been expressed before,” Dr. Lipman says. “It’s like being born with a bone that’s got a weak spot, and is just waiting for years for the right pressure to break.”
If there’s any good news, though, it’s that only 0.6 percent of the U.S. population suffers from antisocial personality disorder, according to a 2007 study. So while there isn’t any conclusive research on how many people carry the genetic tendency for the affliction, it’s likely to be only a very small segment of the population, Dr. Lipman believes. That means that you’re unlikely ever to suddenly commit the sort of violence the DiMaggio allegedly perpetrated.
“Without either a history of violence in his or her life in some form, and/or a genetic predisposition to mental illness of this sort, a person would be much less likely -- significantly, though not zero -- to do something like this,” Dr. Lipman says.