Connecticut school shooting: troubled life of Adam Lanza, a fiercely intelligent killer8040782

But Adam Lanza 's seemingly innocuous life was thrust into the spotlight when authorities said he perpetrated the second deadliest school shooting in U.S. history.

On Friday morning, Lanza walked into Sandy Hook Elementary School in Newtown, Connecticut, dressed in black battle fatigues and a military vest" and began firing, according to a law enforcement source. By the time he was done, 26 were dead -- 20 of them young students.

The bloodshed ended when Lanza 's own life did. He was found dead in a classroom with three firearms: a .223-caliber Bushmaster rifle and two pistols, a Glock and a Sig Sauer.

Before Friday's rampage, authorities said, Lanza killed his mother in their home in Newtown's Sandy Hook community.