In addition to a growing sensitivity to the rights of animals, another significant reason for the increased attention to animal cruelty is a mounting body of evidence about the link between such acts and serious crimes of more narrowly human concern, including illegal firearms possession, drug trafficking, gambling, spousal and child abuse, rape and homicide. In the world of law enforcement — and in the larger world that our laws were designed to shape — animal-cruelty issues were long considered a peripheral concern and the province of local A.S.P.C.A. and Humane Society organizations; offenses as removed and distinct from the work of enforcing the human penal code as we humans have deemed ourselves to be from animals. But that illusory distinction is rapidly fading.

“With traditional law enforcement,” Sgt. David Hunt, a dog-fighting expert with the Franklin County Sheriff’s Office in Columbus, Ohio, told me, “the attitude has been that we have enough stuff on our plate, let the others worry about Fluffy and Muffy. But I’m starting to see a shift in that mentality now.” Hunt has traveled to 24 states around the country in order to teach law-enforcement personnel about the dog-fighting underworld, often stressing the link between activities like dog fighting and domestic violence. “You have to sell it to them in such a way that it’s not a Fluffy-Muffy issue,” he said of teaching police officers about animal-abuse issues. “It’s part of a larger nexus of crimes and the psyche behind them.”…

But the intuitions that informed the narrative arc of Tom Nero are now being borne out by empirical research. A paper published in a psychiatry journal in 2004, “A Study of Firesetting and Animal Cruelty in Children: Family Influences and Adolescent Outcomes,” found that over a 10-year period, 6-to-12-year-old children who were described as being cruel to animals were more than twice as likely as other children in the study to be reported to juvenile authorities for a violent offense. In an October 2005 paper published in Journal of Community Health, a team of researchers conducting a study over seven years in 11 metropolitan areas determined that pet abuse was one of five factors that predicted who would begin other abusive behaviors. In a 1995 study, nearly a third of pet-owning victims of domestic abuse, meanwhile, reported that one or more of their children had killed or harmed a pet.

The link between animal abuse and interpersonal violence is becoming so well established that many U.S. communities now cross-train social-service and animal-control agencies in how to recognize signs of animal abuse as possible indicators of other abusive behaviors. In Illinois and several other states, new laws mandate that veterinarians notify the police if their suspicions are aroused by the condition of the animals they treat. The state of California recently added Humane Society and animal-control officers to the list of professionals bound by law to report suspected child abuse and is now considering a bill in the State Legislature that would list animal abusers on the same type of online registry as sex offenders and arsonists.