It was previously reported that news articles about Norwegian mass murderer Anders Behring Breivik were found in the apartment Lanza shared with his mother, but Thursday the Hartford, Conn., Courant reported sources close to the investigation now say documents related to other massacres were also found in the residence.
Lanza shot and killed 26 people, including 20 children, at Sandy Hook Elementary School on Dec. 14 before taking his own life. He had first shot and killed his mother that day in their home.
Connecticut state police offered an update last week on its investigation to victims' families, Sandy Hook teachers and first-responders and discussed a theory that Lanza was attempting to out-do the other mass killers, the newspaper said.
Danbury, Conn., State's Attorney Steven Sedensky said he expects the final report of the incident will be completed by the end of June.
Notable deaths of 2014 [PHOTOS]