From the report:
Investigators found more than 1,600 rounds of ammunition in the house, and a holiday card with a check "made out to Adam Lanza for the purchase of a C183 (firearm), authored by Nancy Lanza," according to a search warrant.
Last time I checked, a C183 was a camera. It took about... THREE seconds to Google. What kind of mother gives their son a holiday gift of a firearm? This is either completely negligent police / investigation work or piss poor reporting.