Among the details to emerge in the aftermath of the Connecticut elementary school massacre was the possibility that the gunman had some form of autism.
Adam Lanza, 20, had a personality disorder or autism, his brother reportedly told police. Former classmates described him as socially awkward, friendless and painfully shy.
While those are all consistent with autism, a propensity for premeditated violence is not. Several experts said that at most, autism would have played a tangential role in the mass shooting -- if Lanza even had it.
"Many significant psychiatric disorders involve social isolation," said Catherine Lord, director of the Center for Autism and the Developing Brain at New York-Presbyterian Hospital.
Autism, she said, has become a catch-all term to describe anybody who is awkward.
Some type of schizophrenia, delusional disorder or psychotic break would more clearly fit the crime, experts said.
H. Wayne Carver, chief medical examiner in Connecticut, told reporters Tuesday that his team was consulting a geneticist in attempt to determine whether Lanza had a mental illness that might explain help his behavior. Dr. Carver said he could not verify reports that Lanza had Asperger's syndrome, a higher-functioning form of autism, but that the developmental disability "is not associated with behavior patterns that are violent."
The hallmark characteristics of autism are social inability, communication problems, and repetitive behaviors or obsessive interests. It emerges in early childhood and exists on a vast spectrum, from those who bang their head against the wall to those who can recite train schedules from memory.
The rate of autism has skyrocketed over the last two decades, largely because of an expanded definition of the disorder and increasing awareness. The U.S. Centers for Disease Control and Prevention estimates that 1 in 88 children have it.
Researchers have struggled to draw clear lines between the various forms. As a result, the American Psychiatric Association is folding all of its varieties, including Asperger's, into a single diagnosis next year: autism spectrum disorder.
There is more aggression associated with autism than with other disabilities. But it usually amounts to a tantrum and does not involve planning, weapons or an intention to harm anybody.
People with autism are more likely to be victims of violence than perpetrators. Those who are bright -- as Lanza was by several accounts -- often face bullying.
Some wind up in trouble with the law because they are unaware of social convention, and quirkiness or attempts at being friendly get misinterpreted.
John Constantino, an autism specialist at Washington University in St. Louis, said the social detachment and withdrawal associated with the disorder can accentuate other psychiatric conditions that are connected to violence.
And the feelings of isolation often intensify after high school, with the loss of a structured environment that allows many people with autism to stay afloat.
"They sort of fall off this cliff when they don't have a village," Dr. Constantino said.
Lanza finished high school early and was living with his mother. Police said he was disturbed by the divorce of his parents in 2009.
None of that, of course, explains why he killed his mother, 20 elementary school students, six women at the school and then himself.
"The only way somebody could do something like this is if they totally lost touch with reality," said Daniel Geschwind, an autism expert at the University of California, Los Angeles. "Autistic people are not sociopaths."