The man who shot dead 20 children and six adults at a Connecticut elementary school wanted to kill more people than the 77 slain by a Norwegian man in a 2011 rampage, CBS News reported, citing unnamed law enforcement sources.
A Connecticut state police spokesman dismissed the report as inaccurate speculation.
Adam Lanza, 20, who killed himself as police closed in on him at Sandy Hook Elementary School in Newtown, Connecticut, on December 14, saw himself in direct competition with Anders Behring Breivik, who killed 77 people in a bombing and shooting attack in Norway on July 22, 2011, CBS said.
Breivik surrendered to police.
Citing two officials briefed on the Newtown investigation, CBS said Lanza targeted the elementary school because he saw it as the "easiest target" with the "largest cluster of people."
The report did not say how the investigators learned of Lanza's desire to compete with Breivik.
Lanza was also motivated by violent videogames and had spent numerous hours playing games and working on his computer shooting skills in a private gaming room with blacked out windows, CBS said.
Investigators recovered a large number of games from the basement, the report said.
Evidence shows that in his mind, Lanza was likely acting out the fantasies of a video game during his shooting spree with each death amounting to some kind of "score," CBS said.
Lanza killed 20 schoolchildren aged 6 and 7 plus six adults who worked at the school, shocking the United States and leading President Barack Obama to propose new gun control legislation.
Authorities have not publicly spoken of his motive.
"All of it is speculation. There is no basis to the CBS story. We have not established a motive. It's inaccurate," Connecticut State Police Lieutenant Paul Vance said in a statement read on CNN.
Breivik, a self-styled warrior against Muslim immigration, killed eight people by bombing the Oslo government headquarters and then shot dead 69 people at the ruling party's summer youth camp.
A Norwegian judge last year sentenced Breivik to the maximum 21 years in prison, though his release can be put off indefinitely should he deemed a threat to society.