Investigators have determined Lanza did visit a gun range, but they have not determined whether he shot there, officials probing the second-deadliest school shooting in US history said.
Investigators have also learned his mother, Nancy Lanza, visited a gun range on multiple occasions, but they have not determined whether her son was with her during those visits, a spokesperson of the Bureau of Alcohol, Tobacco, Firearms and Explosives was quoted by the ABC News as saying.
ATF agents have been canvassing area gun ranges and gun dealers to learn whether Adam Lanza had been a customer or a visitor.
As with many murder-suicides, the gunman in the Newtown, Connecticut, shooting took to his grave the reasons that compelled him to kill more than two dozen people before taking his own life.
In 2007, a gunman had killed 32 people in a massacre in Virginia Tech, the deadliest shooting incident in the country.
Those who knew the shooter struggled to reconcile the difference between the quiet, withdrawn youngster without a criminal record and the man who donned black fatigues and a military vest and rained hell at Sandy Hook Elementary School last week.
Police identified Adam Lanza as the shooter and that he killed his 52-year-old mother, Nancy, in their home before walking into the school and spraying bullets, killing 26 more people -- 20 of them children no older than 7.
The rampage ended when Lanza apparently took his own life in a classroom. He was carrying three firearms, a semiautomatic .223-caliber rifle made by Bushmaster and two handguns, a Glock and a Sig Sauer. Connecticut law requires gun owners to be at least 21. The guns, authorities said, belonged to his mother.
Police are yet to disclose a motive for the attack -- which left those who knew Lanza trying to discern whether anything in his past could have foreshadowed the present, CNN reported.
