Authorities claim to know the motive behind Mary Winkler's alleged killing of her Tennessee pastor husband, but they won't make it public.
While the 32-year-old mother of three's attorneys hint at psychological problems as a possible defense, definitive answers elude even those closest to her.
However, a psychotherapist and author told "Good Morning America Weekend Edition" that spousal killers tend to follow patterns.
Robi Ludwig, co-author of "'Til Death Do Us Part," said she doesn't believe the Winkler murder was premeditated.
"She's somebody that seems really sick, and that she was not treated," Ludwig said. "I'm not saying she was insane, but she seems like somebody who had, you know, an illness, and was very angry with her husband during one moment in time, and just lost it."
About 11 percent of murder victims between 1976 and 2002 were killed by their spouses or lovers, according to the U.S. Department of Justice. But with every case, people want to know what made the accused kill the person they married.
In her book, Ludwig delves into the mind of the murdering spouse to pinpoint distinct personality types and explain how and why relationships explode into violence. She names 10 different categories of murderers.
She said not enough information is known about Winkler's case to categorize her. She is charged with first-degree murder in the March 22 killing of her husband, Matthew Winkler, a minister with the Church of Christ. She has yet to be tried.
Past cases that already have been judged in the courts, however, reveal patterns behind spousal killers.
Ludwig writes about the "temper tantrum killer" -- individuals who are prone to violent outbursts when their needs are not met. She said Scott Peterson, who was convicted of killing his pregnant wife, Laci, and sentenced to death, is one of these.
There's also the "narcissistic killer," who is someone who harms those who no longer fulfill his needs. She cited Rabbi Fred Neulander, who was convicted of having his wife killed so he could continue an affair. Sentenced to life in prison, Neulander maintains his innocence.
Betty Broderick was the picture-perfect San Diego super mom -- then she lost her husband to another woman and lost custody of her children. Emotionally ravaged, Broderick shot her ex-husband and his new wife to death. Ludwig classifies her as an "abandonment killer."
Christian Longo is now on death row for killing his wife and children. Before the murders, he moved his family across the country, trying to escape a string of bad checks and forgery charges. Ludwig said Longo is a "sociopathic killer," which she describes as a charming individual who knows the difference between right and wrong but doesn't care.
While people kill for many different reasons, they all have one common denominator, said Ludwig.
"I think it's that at that moment in time, during the murder, the person is only thinking of themselves," she said. "And very often they feel like they are the victim, and the other person is causing them pain, and they don't have the resources to deal with it any other way."