Connecticut law enforcement authorities have discovered a detailed spreadsheet that shows Adam Lanza plotted the shootings at Sandy Hook Elementary School and researched mass murders for years, the New York Daily News reported.
"What investigators found was a chilling spreadsheet seven feet long and four feet wide that required a special printer, a document that contained Lanza's obsessive, extensive research -- in nine-point type -- about mass murders of the past, and even attempted murders," the newspaper said.
Hearst Connecticut Newspapers previously has reported that investigators found reams of material that showed Lanza's obsession with other mass murders and that investigators believe he had plotted his Dec. 14 rampage for some time.
The Daily News story attributed the information to an unnamed veteran police officer who attended last week's International Association of Police Chiefs and Colonels midyear meeting in New Orleans. At the meeting, Col. Daniel Stebbins, of the Connecticut State Police, briefed other high-ranking police officials on the investigation into the shootings, when Lanza, armed with an AR-15 Bushmaster semi-automatic rifle and two handguns, killed 20 first-graders and six adults at Newtown's largest elementary school.
Before driving to the school, Lanza first shot and killed his mother, Nancy, in the Yogananda Street home they shared.
The source told the Daily News that investigators believe the spreadsheet was in reality a video game score sheet, one that the 20-year-old mass murderer wanted to have his name atop, and that he picked the school because it gave him the best chance to rack up the greatest number of "kills."
He also said that investigators now believe Lanza had planned the massacre for years.
Connecticut State Police spokesman Lt. J. Paul Vance issued a statement Monday morning saying that police would not be releasing any further information on the case. Stebbins' comments at the New Orleans seminar were intended "for law enforcement professionals only," and should not have been made public until the families of the victims had been briefed, Vance said.
"Following every tragic mass murder incident in this country, it is customary for law enforcement to share their lessons learned from the investigation," Vance said. "It is unfortunate that someone in attendance chose not to honor Col. Stebbins' request to respect the families' right to know specifics of the investigation first."
But unlike some previous instances when information about the shootings and Lanza's possible motivation were reported by the news media, Vance didn't dispute the accuracy of the story.
He said a final state police report is "still several months away."
Earlier this month, Hearst reported that State Police investigators had recovered from Lanza's home what a source described as documents related to "virtually every mass murder" in the United States and abroad.
Lanza showed particular interest in the October 2006 shooting at a one-room Amish schoolhouse in Lancaster County, Pa., in which gunman Charles Carl Robert IV took hostages and shot 10 schoolgirls, five of them fatally, before killing himself.
Lanza also had researched Anders Behring Breivik's shooting spree in Norway in July 2011. Breivik killed 77 people, eight of them by setting off bombs in downtown Oslo, before he shot and killed 69 others, many of them teenagers, at a summer camp on Utoya island in July 2011.
Investigators have theorized that Lanza wanted to exceed Breivik's death toll, sources told Hearst.