PHOENIX (AP) -- As an 8-year-old Arizona boy sits in a juvenile jail, charged with murdering his father and another man, the biggest unanswered question is "Why?"
Police say the boy planned and meticulously carried out the shootings, but they haven't discussed a motive. Child psychologists and others say that while many factors could cause a child to kill a parent, the most common in other cases has been severe abuse.
No homicides were committed in the United States by a child 8 and younger between 2005 and 2007, according to FBI statistics. Twenty-one children ages 5 to 8 did so in the 10-year period ending in 2004, the statistics show.
"These are head-scratchers, especially when you have young people," said defense attorney Paul Mones, who has represented children accused of killing their parents and written a book called "When a Child Kills."
He said that when it does happen, the overwhelming majority do so for one of a handful of reasons -- mental health issues within the family, or physical, emotional or sexual abuse in the home.
"Many of these kids who commit homicides suffer from some level of traumatic stress disorder," Mones said. "They're living in an environment that is oftentimes extremely dysfunctional, oftentimes violent."
In Ohio, for instance, a 13-year-old boy told a judge in a 2000 case in Cleveland that he shot his father with a revolver in self-defense because of years of abuse that included beatings with hangers and mop handles.
A 12-year-old boy from Douglas, Ariz., is accused of fatally shooting his mother following an argument in August. Defense attorneys say the boy was verbally and physically abused.
James Alan Fox, a criminologist at Northeastern University in Boston, said in very rare cases, children kill because they don't have a conscience. They are "the so-called bad seeds ... who are capable of committing murder without feeling an emotional response," he said.
"More often these children are responding to events in their lives," Fox said. "It's usually physical abuse of some sort. It can be to protect themselves or another family member against physical or sexual abuse, and less often is a reflection of severe mental illness."
St. Johns, Ariz., police Chief Roy Melnick said last week that investigators were looking into whether the boy in the latest case might have been abused, although he later told some media outlets they have found no evidence of that. Melnick said the boy confessed to the shootings but wouldn't discuss specifics.
A gag order has been imposed on the boy's attorney and others involved in the case, but the attorney previously claimed police questioned the child without representation from a parent or attorney and didn't advise him of his rights.
Those who know the boy and his family say there was no abuse -- that his father, Vincent Romero, was a good dad trying to raise his son to be polite and respectful.
Hundreds of mourners packed a funeral Mass on Monday for Romero. The funeral for the other victim, Timothy Romans, who rented a room from Romero, was scheduled for Saturday.
Romans' wife, Tanya, said her husband lived with Romero in St. Johns during the week because of his construction job but returned to his family in metropolitan Phoenix on weekends. Romero and Romans were co-workers.
Tanya Romans said her husband closely followed their teenage daughters' sporting events and sent his love through calls and text messages regularly.
"I can't imagine myself being without my husband," she said Tuesday. "He would always call me even though he worked far away."
She declined to discuss the investigation into her husband's death.
Prosecutors said there was no record of any complaints filed about the boy with Arizona Child Protective Services and that the youngster had no disciplinary record at school.
Another factor often found among children who kill is a broken home, said Robert Heckel, professor emeritus in psychology at the University of South Carolina and co-author of "Children Who Murder: A Psychological Perspective."
"The thing that stands out and is present in many if not most of these cases is a broken home, a disrupted family situation," Heckel said.
In the Arizona case, the boy's parents were divorced. Romero had full custody and the boy's mother, Eryn Thomas, lives in Mississippi, although she had been in St. Johns for a visit the weekend before the shooting. Romero recently remarried.
Heckel said it's only a matter of time before the motive is revealed.
"There are not that many mysteries," said Heckel, who is not involved in the case. "I would not be surprised if there's some pretty reasonable explanation and understanding of what happened -- it's just a matter of digging."