Colorado and New York also passed new gun control requirements in the wake of the Newtown shooting, in which a 20-year-old gunman used a military-style semi-automatic rifle.
Investigators are also trying to determine who owns a number of guns that were found at the home, including a semi-automatic military-style rifle, the Associated Press news agency reports.
The attorney general said a search of Spyropoulos' home turned up two semi-automatic handguns, a shotgun and a rifle that police described as an assault weapon.