People have been shocked by the Cleveland kidnapping and with good reason; what can bring a person, Ariel Castro, to kidnap three victims, Amanda Berry, Gina DeJesus and Michelle Knight, at different times and keep them enslaved for years?
Ariel Castro, like most known kidnappers, was a reclusive person with some minor brushes with the law. We know he has a violent history against the former spouse and children, but the charges were eventually dismissed by the courts. He had been recently been fired from his school bus driving job; one of his daughter is in jail for the attempted murder of her own daughter; both his brother have some family violence entries. This information do not tell us much about Ariel Castro and we are still left with the puzzle to explain the jump from a poorly socially integrated individual to a decade long multiple victims kidnapping.
What we know about kidnappers is not much. We know that pre-existing history is hit-and-miss, sometimes providing relevant information, sometimes not. They are often solitary, have psychological problems, poor social skills, they are not socially stable (although Ariel Castro was employed), and they found it difficult to cope with life. They tend to have a grandiose sense of themselves, but their aspirations and self-perceptions often go well beyond their abilities and skills; in other words, their emotional and intellectual capacities do not square up with their desires. Kidnappers are not physically or mentally lacking, but are short tempered and impulsive and they may make poor decisions; in other words they do not seem different from the garden variety psychopath or the frequent law breaker.
Most kidnappers tend to act alone; the Paul Bernardo and Karla Homolka duo seem to be more the exception than the rule.
Psychologically, kidnappers tend to have violent and sadistic fantasies and often picture themselves living their fantasies in real life; this is probably the quality jump we were looking for. Most people can watch a movie or day dream but realize it is a movie or a passing wish; sexual-predator-kidnappers want to live their own fantasies. Sexual sadism is the label that comes to mind when thinking of Ariel Castro, at least based on what can be inferred by the news.