One of my colleagues, Dr. Bruce Perry, is senior fellow at the Child Trauma Academy and a child psychiatrist who has worked with or consulted on cases involving both children exposed to extreme violence and young perpetrators. He consulted with authorities guiding the response to Columbine.

To be clear, no one can diagnose a patient from afar, and there are too many unknowns in this case to diagnose Lanza. Still, for academic purposes and to the point of accurate mental health discussion and addressing ideas about identifying at-risk individuals, Perry says of the shooter: "My first thought was that he might have had a psychotic break -- and that his odd, disengaged behaviors earlier in life -- reasonably labeled as something like an ASD by some -- might actually have been prodromal psychotic disorder."

Schizophrenia is often not diagnosed until a first psychotic episode occurs, typically in the late teens or early 20s. These episodes are marked by delusions, hallucinations (mainly auditory), and often extreme paranoia. But long before these occur, some children who ultimately develop the disorder seem "off" and retreat from social contact. This is part of a set of symptoms known as a "prodrome" because it precedes those that characterize the later illness.

Like autism, schizophrenia is now believed to be a condition involving differences in early brain development, which probably begin in the womb, even though symptoms may not appear until years or even decades later. Lanza was 20, which is right in the typical range for a first psychotic episode to occur. But that is the most we can say.

Early symptoms of schizophrenia can sometimes be indistinguishable from those of autism: they include social withdrawal; communication problems and restricted speech; odd, repetitive behavior; an apparent lack of emotion or emotional expression and often, lack of conformity in terms of hygiene and dress. In both cases, the symptoms can start in early childhood, though with schizophrenia, there is often a noticeable exacerbation of prodromal symptoms in the year or two before the first psychotic episode.

Jorge Dan Lopez/Reuters Jorge Dan Lopez/Reuters

Both conditions are also sometimes linked with extremely high intelligence, which makes our failure to provide effective help even more wasteful. Lanza was an honors student, whom some of his classmates labeled a "genius." He was known to dress formally and carry a briefcase, not the backpacks favored by most schoolchildren. In some instances then, because we don't have biological markers to provide a definitive diagnosis, it may be impossible to tell if someone has an ASD or is going to develop schizophrenia until psychosis itself occurs.

Indeed, some of the same genes that have been linked to autism risk are also linked to schizophrenia risk -- and some of the same environmental triggers also raise risk for both. For example, having an older father or being in the womb while your mother suffers from certain infections elevate both the risk of autism and schizophrenia. It is not known why the predisposition becomes one disorder rather than the other.