(CBS) On June 16, 2005, 15-year-old Nakisha Waddell took the stand in a Virginia courtroom and tried to explain why she'd murdered her mother.
"It's from all the years of fighting and fussing," said Nakisha, her voice so low the judge had trouble hearing her. "You could only take so much before you finally explode."
And explode Nakisha did. Thirteen months earlier, when she was just 14, the former Girl Scout stabbed her mother Vaughne Thomas 43 times, inflicting dozens of wounds that sunk six inches into the woman's neck, chest, back and face.
Once her mother was dead, Nakisha and her then-15-year-old friend Annie Belcher, who also pleaded guilty for her role in the murder, dug a hole in the backyard and put Vaughne's body inside it. The girls poured rubbing alcohol and nail polish remover on Nakisha's mother and tried to set her on fire. When that didn't work, they poured a crude concrete mixture atop the body and covered it with leaves and logs.
When her defense attorney asked Nakisha if she was mentally ill at the time of the murder, she said no.
"I stabbed her because I was mad," she said.
It is a particularly unsatisfying response to a particularly gruesome crime. There was no indication that Vaughne - or Nakisha's step-father - had been abusive. For the past few weeks, Nakisha recalled, the two had been bickering constantly - mostly over the unsteady presence of Nakisha's biological father in her life. On the last day of her life, mother and daughter argued because Vaughne found Nakisha home when she should have been at school.
How did such a commonplace set of arguments end in murder? At the sentencing hearing, prosecuting attorney Keith Blankenship put it this way: "There is something gravely wrong with Ms. Waddell." And even now, almost seven years after his client was sentenced to 70 years in prison, Nakisha's defense attorney Roy David Warburton can only say that Nakisha and Annie were "troubled young ladies."
But while we may never know for sure what led Nakisha to commit such a taboo and violent act, we do know that the crime itself, known as matricide (the killing of a mother by her child) - or more broadly, parricide (the killing of a parent by his or her child) - is relatively rare, poorly understood and, according to recent data, on the rise.
In November 2011, the Department of Justice released its annual homicide statistics, which revealed that while homicide across the country has fallen in almost every other category since 1980, the number of parents killed by their children is growing as a percentage of family homicides. In 2008, FBI data show that at least 117 mothers were killed by their children, and according to statistician Erica Smith at the Bureau of Justice Statistics, that number could be as high as 260, which would make it the highest number of matricides since 1991.
Joanne Witt probably didn't know any of this when she was stabbed to death in her bed on June 12, 2009. Witt, 47, was a single mom who had reportedly had a contentious relationship with her 14-year-old daughter Tylar for years. But like Vaughne Thomas, it's unlikely she could have fathomed that her barely teenage daughter - along with the girl's 19-year-old boyfriend - was capable of murder.
In August 2011, Tylar was sentenced to 15 years in prison for her role in her mother's murder, while her boyfriend, Stephen Colver, got life. For more details about Witt's murder, including who actually held the knife that night, watch 48 Hours this Saturday.
According to Kathleen Heide, a professor at the University of South Florida who has researched and written extensively on the subject of matricide, the crimes committed by Nakisha and Tylar illustrate several "knowns" about young girls who kill their mothers.
First, says Heide, the average age for teen girls to commit matricide is between 14 and 17. In addition, according to Heide's analysis of matricide cases between 1976 and 2007, 44 percent of the girls who kill their mothers did so with the aid of an accomplice.
"To take that step girls may need the support of someone else," says Heide, "whereas boys tend to be more autonomous."
And there are other things we know about these cases: first, killers like Nakisha are very rare. According to Heide's research, "boys outnumbered girls seven-to-one in the killing of mothers." And most parents killed by their children are killed by adult children; only about 17 percent of parricide perpetrators are under 18 years old.
When it comes to why girls commit this crime, the answers are less clear. Heide has written that parricide perpetrators, male and female, tend to have been either severely abused, severely mentally ill or "dangerously anti-social."
By most accounts, neither Nakisha nor Tylar were severely abused or mentally ill, suggesting they may fall into the latter category, which Heide describes as including people who "kill for selfish reasons, like freedom or money."
Finally, Heide and Paul Mones, the author of "When A Child Kills: Abused Children Who Kill Their Parents," agree that in parricide cases, there is often an element of "overkill." Nakisha stabbed her mother 43 times, and Joanne Witt was stabbed more than 20 times, her head nearly severed by the knife used to kill her.
Heide explains that when a child kills a parent, they sometimes enter an "altered state of consciousness" and later report being "astonished" by the intensity of their actions.
"When they finally get to that point, there's a great deal of anger buried deep inside and the anger fuels the release of stress hormones which feeds the aggression," Heide says. "They'll continue stabbing or bludgeoning until they're exhausted...They may not be making 30 conscious decisions to stab."
"In that heightened state of emotional arousal," she says, "there is a great deal of anger at the core."
But whether the motivation to kill a mother comes from anger, abuse, illness or greed, there is no doubt that the modern history of matricide is full of horror stories that rivet: In Massachusetts in 1892, Lizzie Borden famously murdered her father and step-mother, a story immortalized, improbably, in a children's rhyme: Lizzie Borden took and ax/and gave her mother 40 whacks... In 1954, two New Zealand teens named Pauline Parker and Juliet Hulme murdered Pauline's mother; their story became the movie "Heavenly Creatures" starring Kate Winslet. And in 1990, 14-year-old Gina Grant bludgeoned her alcoholic mother to death with a candlestick. Grant made national headlines in 1995 when she was admitted to Harvard and then had her admission rescinded when the university learned of her past crime.
Currently, Georgia's Rockdale County District Attorney's office is preparing to try twin teenage girls Tasmiyah and Jasmiyah Whitehead for the beating and stabbing death of their mother in January 2010. According to Richard Reade, the DA prosecuting the case, the girls, who will be tried as adults on charges of first degree murder, come from a family with "four generations of family dysfunction."
Of course, not every dysfunctional family ends up imploding so spectacularly. But when they do, Heide says that society can't help but pay attention.
"Because girls are less likely to have violent solutions than boys, the fact that a daughter would take her mother's life shocks people, it's horrifying to them," she says. "It feels personal because most people are parents. You can't help but wonder, could my child do that?"