Family and friends remember Adam Lanza as many things - intelligent, nerdy, goth, remote and thin.
Now the world will remember him as a mass murderer. The 20-year-old man is believed to have killed his mother, gunned down more than two dozen people, 20 of them children, at a Connecticut grade school and committed suicide.
Law enforcement officials say he might have suffered from a personality disorder.
Authorities have not spoken publicly of any possible motive. They've found no note, and Lanza had no criminal history. Witnesses said the shooter didn't utter a word.
Now investigators are trying to learn all they can about Lanza. They've questioned his older brother, Ryan, who is not believed to have any involvement in the rampage and hadn't had contact with Adam Lanza since 2010.