In the aftermath of the tragic shooting in Tucson this week, there are lessons for preventing another mass casualty attack.
That's what the brother of Unabomber Ted Kaczynski told ABC News Monday night, as he digested descriptions of alleged shooter Jared Lee Loughner's behavior that carried echoes of his own experience.
"We can't undo the crime," David Kaczynski said. "What we can do is try to understand how and why it occurred. And maybe look for ways we could prevent it."
The alleged shooter's growing isolation and erratic behavior, as detailed in news accounts, are familiar as hallmarks of a "lone wolf," a personality type that has the potential to be lethal. But David Kaczynski believes the suspect in the Tucson shooting also carries many of the same symptoms of schizophrenia that his brother exhibited as he set out on a bombing spree that killed three and injured 23 others.
CLICK HERE TO WATCH A NIGHTLINE SEGMENT ON LONE WOLF KILLERS
"It brings back horrible memories and some sense of recognition," said David Kaczynski, who eventually recognized the writings of the Unabomber as those of his brother and alerted authorities. "I think when we talk about a lone wolf we have to make distinctions -- people like my brother, my brother was not just a lone wolf, he was diagnosed with very serious mental illness, schizophrenia. And this case, from what little I know, from what I can tell, has schizophrenia written all over it."
Kaczynski stressed that most people with mental illnesses are not violent. But there are cases, he said, "where the psychotic delusions precipitate psychotic behavior and it's very, very difficult to predict."
Kaczynski believes one troubling sign for his brother was his increasing isolation.
David and his brother Ted grew up together in Chicago in what seemed to be model family. Ted was an academic prodigy who was accepted to Harvard at age 16. But there were worrying signs -- and denial. In an interview after the Virginia Tech shootings, David told Nightline's Martin Bashir, "There was probably a time when I asked my mom, 'What's wrong with Teddy?' and she said, 'What do you mean? There's nothing wrong with your brother.'"
When David Kaczynski looked at his brother, he saw an isolated, sensitive individual who had problems socially. In 1971, Ted Kaczynski moved to a remote cabin in Montana that lacked electricity and running water. He lived as a recluse. At one point, he did reach out for help. He wrote to the country health office, recalls David Kaczynski, "to see if he could do psychological counseling through the mail and he got a polite letter back saying that this was not possible. ...The end result was that this man who was very ill, [who] needed some help, was essentially turned away."
Monday night, David Kaczynski heard reports that Loughner, too, had over the past year retreated from society, terminating friendships and getting kicked out of school.