(CBS News) The search for a motive behind the shooting is proving to be difficult. A computer and hard drive recovered from gunman Lanza's home were smashed into so many small pieces, that the FBI lab has been unable to retrieve any useful data. Cyber experts are not optimistic.
Police are searching credit card, email, and phone records for Lanza and his mother. Investigators are also trying to reconstruct Lanza's Internet searches.
But officials say Lanza was a socially-awkward recluse who had little touch with the outside world. And he killed his mother, Nancy Lanza, the one person who knew him best.
Law enforcement officials say over the past three years, his mother bought and registered the three semi-automatic weapons Lanza carried with him during his attack at Sandy Hook Elementary School.
Sources say a gun trace revealed Nancy Lanza bought the murder weapon -- a Bushmaster AR-15 -- in March 2010.
A year later, in March 2011, she bought a 9mm Sig Sauer pistol. That gun was found in one of pockets of Lanza's cargo pants.
The third gun, the Glock 10 mm that Adam Lanza used to take his own life, was purchased eleven months ago in January 2012.
Lanza did not buy any of the weapons himself. But agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives have confirmed he and his mother did go shooting together at various gun ranges.