(CNN) -- After nearly a year, the motive behind last December's massacre at a Connecticut's Sandy Hook Elementary School remains unknown, state authorities reported Monday.
Connecticut officials have released a 44-page summary of the investigation into the second-deadliest shooting in U.S. history, outlining how the gunman, identified as 20-year-old Adam Lanza, killed his mother, then stormed the elementary school and killed himself as police arrived. But Lanza never gave anyone "any indication" of what he planned on December 14, 2012.
"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," the report states.
Police arrived at the school less than four minutes after the first 911 call. One minute later, Lanza killed himself.
"In fewer than 11 minutes twenty first-grade pupils and six adults had lost their lives," the report states.
Victims' family members were informed of the report, said Mark Dupuis, a spokesman for Danbury State's Attorney Stephen Sedensky, whose office conducted the investigation.
Dupuis declined to provide details about when, where, and how the families were given the details of the report.
"We are sensitive to the needs of the families, and those needs are being addressed," Dupuis said.
The family of Victoria Soto, a teacher who shielded her students before being shot to death, said the release of the report is "yet another blow that our family has been dealt."
A statement from the family said, "While others search for the answer as to why this happened, we search for the how. How can we live without Vicki? How do we celebrate Christmas without Vicki? How do we go on every day missing a piece of our family? Those are the questions we seek the answers for. There is nothing in the report that will answer those for us."
The report, which is available on the Connecticut Division of Criminal Justice website, is separate from a much longer evidence file that Connecticut State Police will release at an unspecified date.