HARTFORD, Conn. — A report on the Newtown school shooting says that the gunman had an obsession with mass murders but that investigators did not discover any evidence he had indicated to others an intention to carry out such a crime.

The summary of the investigation by Connecticut State’s Attorney Stephen Sedensky says Adam Lanza was obsessed in particular with the April 1999 shootings at Columbine High School in Colorado.

The report on the Dec. 14 massacre of 20 children and six adults says the question of Lanza’s motive may never be answered conclusively.

Lanza killed his mother inside their Newtown home before driving to Sandy Hook Elementary School and carrying out his rampage. He committed suicide as police arrived.