20-year-old gunman Adam Lanza acted alone and did not conspire with anyone else before killing his mother, and then shooting to death 26 children, faculty and then himself at Sandy Hook Elementary School in Newtown, Connecticut on December 14, 2012, USA Today reported.  

A Connecticut State Police report revealed that Lanza's motives remained unknown, in which he perpetrated one of the worst school shootings in U.S. history. 

The 48-page summary report of the mass shooting was prepared by lead investigator, State's Attorney Stephen Sedensky III.

Lanza "shot his way and first killed Principal Dawn Hochsprung and school psychologist Mary Sherlach in the north hallway. Lanza also shot two other staff members in the hallway who survived. He then went into two classrooms and killed 20 children and four teachers," the report said. He also used a Bushmaster XM15-E2S rifle to kill the victims before shooting himself to death with a Glock 10mm handgun. News reports said that he killed his mother in her bed with a .22 caliber rifle.

The report also detailed the series of events by Lanza:  "The shooter walked normally, did not say anything and appeared to be breathing normally," it read.

"The vast majority" of people who knew Lanza anad were interviewed by police still remain unsure why he committed the shootings. An autopsy of Lanza also revealed that "no drugs were found in his system," USA Today also reported.

The report said in addition to his Bushmaster and Glock handgun, Lanza was also armed with a Sig Sauer 9 mm pistol and a large supply of ammunition, USA Today also reported. All of the firearms were legally purchased by his mother. It was revealed that Nancy Lanza, the gunman's mother, wanted to buy her son a CZ 83 pistol for Christmas.