FILE - This undated file photo circulated by law enforcement and provided by NBC News, shows Adam Lanza. Authorities say Lanza killed his mother at their home and then opened fire inside the Sandy Hook Elementary School in Newtown, killing 26 people.
People close to the investigation tell The Associated Press that the gunman in the Sandy Hook Elementary School massacre showed interest in other mass killings.
Twenty-year-old Adam Lanza killed his mother at their home before killing 20 first-graders and six staff members at Sandy Hook Elementary School in Newtown on Dec. 14. He killed himself as police arrived.
A law enforcement official briefed on the investigation says authorities found literature on other mass shootings at Lanza's house. Another person familiar with the investigation says Lanza showed an interest in other mass murders. They spoke on condition of anonymity because the investigation is continuing.
According to a report in the Connecticut Post, investigators found documents related to several mass murders in the U.S. and overseas. Lanza had a large amount of material related to the 2006 mass murder in an Amish schoolhouse in Pennsylvania, a source told the paper. In that incident, Charles Carl Robert shot 10 girls in the school, killing five, before killing himself.
A police report is expected around June. State police have declined to comment.