WASHINGTON – The 20-year-old man who carried the shooting at Sandy Hook Elementary School reportedly was obsessed with a Norwegian mass murderer, who killed 77 people in 2011.

Law enforcement sources tells CBS News that Adam Lanza was motivated by violent video games and the goal of killing more people than Anders Breivik, who fatally shot 69 people — including teenagers at a summer camp — after setting off a bomb that killed eight people in Oslo.

Two officials who have been briefed on the Newtown, Conn., investigation tell CBS News that Lanza wanted to top Breivik’s death toll and opened fire at Sandy Hook because it was the “easiest target” with the “largest cluster of people.”

Sources also say Lanza may have been acting out video game fantasies.

Twenty first-graders and six adults were killed at the Newtown, Conn., school. Lanza also shot his mother, Nancy, according to police.

Police have not revealed a motive for the attack. But authorities have reportedly recovered a “trove” of video games from the basement of the home Lanza shared with his mother.

Authorities believe he spent many hours there by himself, working on his computer shooting skills.

Lt. J. Paul Vance of the Connecticut State Police tells CBS News the investigation into the motive for the shooting has not been officially completed. He says any statements about the shooter’s intent are speculation.

WTOP’s Mitchell Miller contributed to this report. Follow Mitchell Miller and WTOP on Twitter.