The final report of the State Attorney summarizing the investigation into the shooting was published on November 25 , 2013 . It concluded that Adam Lanza had acted alone , and that the case was closed . The report noted that " Lanza had a familiarity with and access to firearms and ammunition and an obsession with mass murders , in particular the April 1999 shootings at Columbine High School in Colorado . " The report did not identify a specific motive for the shooting , stating , " The evidence clearly shows that the shooter planned his actions , including the taking of his own life , but there is no clear indication why he did so , or why he targeted Sandy Hook elementary school . " On the question of Lanza 's state of mind , the report noted " significant mental health issues that affected his ability to live a normal life and to interact with others , even those to whom he should have been close ... What contribution this made to the shootings , if any , is unknown as those mental health professionals who saw him did not see anything that would have predicted his future behavior . " The report found no evidence that Lanza had taken drugs or medication that would have affected his behavior , and observed , " ' Why did the shooter murder twenty-seven people , including twenty children ? ' Unfortunately , that question may never be answered conclusively , despite the collection of extensive background information on the shooter through a multitude of interviews and other sources . " On December 27 , 2013 , police released thousands of pages of documents pertaining to the investigation . In accordance with law , the names of victims and witnesses were redacted or withheld . The summary report included information about items found on Lanza 's computer equipment , including writings and material about previous mass shootings . A former teacher of Lanza 's noted that he exhibited antisocial behavior , rarely interacted with other students , and was obsessed with writing " about battles , destruction and war . " The Report of the Office of the Child Advocate concluded : " There was not one thing that was necessarily the tipping point driving Lanza to commit the Sandy Hook shooting . Rather there was a cascade of events , many self-imposed , that included : loss of school ; absence of work ; disruption of the relationship with his one friend ; virtually no personal contact with family ; virtually total and increasing isolation ; fear of losing his home and of a change in his relationship with Mrs. Lanza , his only caretaker and connection ; worsening OCD ; depression and anxiety ; profound and possibly worsening anorexia ; and an increasing obsession with mass murder occurring in the total absence of any engagement with the outside world . Adam increasingly lived in an alternate universe in which ruminations about mass shootings were his central preoccupation "
April 1999 shootings
Columbine High School massacre
Sandy Hook Elementary School shooting