(Newser) – Adam Lanza drew motivation from Norway's most notorious mass murderer when he opened fire at Sandy Hook Elementary School, CBS News reports by way of two sources. The officials, who have been briefed on the investigation, say Lanza considered himself in competition with Anders Breivik, who bombed and gunned down 77 people in July of 2011. Wanting to out-kill Breivik, Lanza picked Sandy Hook as the "easiest target" containing the "largest cluster of people."

Lanza had honed his shooting skills by obsessively playing video games in the basement of his family home, and may have considered his death toll of six adults and 20 first graders to be a kind of "score." He also practiced shooting real guns with his mother at a shooting range. The sources were light on details, but said investigators have uncovered evidence of Lanza's obsession with Breivik. But Lt. J. Paul Vance told CBS News that the investigation is ongoing and that any revelations about motive are just speculation. (Read more Adam Lanza stories.)

