Esteban Santiago, the 26-year-old man held in the fatal shootings last week at Fort Lauderdale's airport, reportedly has a history of mental difficulties and it's tempting to assume they explain the crime. Experts say: Don't.
"There is no one explanation that will fit this case or any case," says criminologist James Alan Fox of Northeastern University, an expert on violence.
While mental health troubles could turn out to play a role in the case, it's unusual for symptoms to drive violence, says Edward Mulvey, a psychologist at the University of Pittsburgh School of Medicine who studies violence and mental illness.
There has been no public explanation of a motive for the crime, and terrorism has not been ruled out. It could be that mental illness played no role — it is unclear if Santiago had been formally diagnosed with any mental condition or was undergoing treatment.
A few reported details suggest he was troubled. The mother of the Iraq war veteran said he had been deeply shaken by seeing a bomb explode next to two friends while serving in Iraq in 2010, and relatives said he seemed different when he returned from service.
Santiago's brother Bryan said Esteban told him last August that he was hearing voices and felt he was being chased. In November, he walked into an FBI field office in Alaska and said the federal government was controlling his mind and forcing him to watch Islamic State videos, authorities said.
At that point, officials seized his handgun and had him formally evaluated. After four days he was released and his gun was returned.
But none of these details, by themselves or even together, are enough to draw conclusions, experts say.
Plenty of people have had such experiences in their past and don't commit mass murder, Fox said. The fact that Santiago was released after the evaluation indicates authorities believed he was not dangerous to himself or others, Fox said.
"There's a difference between being psychotic and being dangerous and psychotic," Fox said.
While certain factors often show up in the history of mass murderers, like a history of failure, a tendency to blame others and social isolation, they also appear in the histories of people who don't harm anybody, Fox said. That's why mass killers can't be reliably identified in advance of the crime, he said.
Dr. Paul Appelbaum, a professor of psychiatry at Columbia University in New York, also warned against jumping to the conclusion that a psychiatric disorder is the reason for the shootings. Most behaviors have multiple causes, he said. And even if Santiago suffered from psychosis when he walked into the FBI office, symptoms wax and wane, Appelbaum said, so it's not clear what his situation was at the airport.
In any case, even if had had a psychotic disorder, "most people with psychotic disorders never hurt anybody at all.... There may still be other influences on him that affected his behavior in a material way," Appelbaum said.
Santiago had other recent stresses. He recently became a father, he said in court Monday he hadn't worked since November, and he had no money.
Mulvey said there are people who are driven to violence by delusions, but "they're rare, they're much less common than people might expect." Often when psychotic people are involved in violence it's not because of their mental illness but rather something else, like substance abuse, he said.
The American Psychological Association says that while there's a small association between mental illness and violence directed at others, the overwhelming majority of people with serious mental illness don't pose a risk to others and should not be stereotyped as dangerous.