A report on the mass shooting at a U.S. school in Connecticut says the gunman had an obsession with mass murders, but says his exact motive may never be known.
The state attorney's report, released Friday, said 20-year-old Adam Lanza acted alone in killing 20 school children and six adults at Sandy Hook Elementary School in Newtown, Connecticut last December. Lanza killed his mother before attacking the school. He ended his rampage by shooting himself.
The report says there is evidence that Lanza planned the mass shooting but no evidence that he discussed his plans with anyone else.
Investigators found that Lanza was preoccupied with mass killings, particularly the 1999 massacre at Columbine High School in Colorado.
The report says Lanza had significant mental health issues, but says it is not known how that might have contributed to the shootings.
The violence led the White House to push for major reforms in gun control laws, but the measures filed to gain Congressional approval.