Sandy Hook Killer Adam Lanza: 'Deeply Disturbed Kid, Couldn't Feel Pain'

"He was smart,” the insider said. “He was like one of these real brainiac computer kind of kids.”

Another family friend said Lanza had a condition where he couldn't feel pain.

“A few years ago when he was on the baseball team, everyone had to be careful that he didn’t fall because he could get hurt and not feel it,” the friend told the Daily News. “Adam had a lot of mental problems.”

Adam's father, Peter Lanza, is an executive at GE Energy Financial Services and lives in Stamford with his second wife. He and Adam's mother, Nancy, divorced in 2010. That's also reportedly the last time Ryan Lanza, a rising star at the huge accounting firm of Ernst & Young, saw his brother.

Nancy Lanza had previously worked at Sandy Hook but several sources said they believed she was more recently spending her days caring for the troubled Adam.

Tragically, the three weapons Adam carried into the school on the day of his massacre -- a Glock and a Sig Sauer, both semi-automatic handguns, and a 223 Bushmaster, a military style assault weapon -- all were owned by and registered to Nancy Lanza.