But when the Lanzas finalized their split in 2009, they did have concerns about the care of their then-17-year-old son Adam, according to the pair's divorce mediator.
"The only two things I remember them saying is that she really didn't like to leave him alone and I know they went out of their way to accommodate him," their divorce mediator, Paula Levy, tells the Associated Press.
According to Levy, the Lanzas said their son had been diagnosed with Asperger syndrome, an autism spectrum disorder.
"They worked together about it," Levy adds. "The mom, Nancy, pretty much said she was going to take care of him and be there as much as he needed her, even long-term."
The issue of whether Adam has Asperger's is a heated one, with many mental-health experts suggesting there is no connection between autism and a propensity for violence – even though Adam, three years after the divorce, killed his mother and shot 26 others during the school massacre in Connecticut.
Many experts say the idea that people on the autism spectrum are incapable of empathy is oversimplified and often flat-out false. They are said to be no more likely to commit violent crime than other people, and in fact are vastly more likely to be the victims of violent crime than others.
The divorce papers came to light as police continued to search for a motive. New information from investigators reveals that Adam smashed the hard drive of at least one of his computers at home before he set off on his rampage. It is not clear if information could be retrieved
According to court papers, Nancy Lanza filed for divorce on Dec. 9, 2008, in Stamford, Conn., with the legal boilerplate reason that "the marriage has broken down irretrievably and there is no possibility of getting back together."
Nancy and Peter Lanza had been married for more than 27 years and had two sons. Adam's older brother Ryan was born in 1988.
The action was finalized on Sept. 23, 2009, with Peter, an executive making $8,556 a week, agreeing to pay $240,000 a year in alimony, with built-in increases yearly.
Nancy would have primary custody of Adam in their Sandy Hook home, but Peter would get "liberal visitation and vacations" and pay the college costs of both his sons, the papers say. Peter has since remarried.
Peter said in a statement over the weekend after the shooting, "No words can truly express how heartbroken we are. We are in a state of disbelief and trying to find whatever answers we can."