Investigators are planning to release a long-awaited report on the Newtown school shooting, nearly a year after the massacre of 20 children and six women inside Sandy Hook Elementary School.

The summary report by the lead investigator, State's Attorney Stephen Sedensky III, could provide some of the first official answers to questions about the history of the gunman and the police response to one of the worst school shootings in American history.

The Dec. 14 shooting plunged the small Connecticut community into mourning, elevated the divisive issue of gun control to the top of President Barack Obama's domestic agenda and led some states to impose tougher gun laws. It sparked debates on school safety and the U.S. mental health system.

The report expected Monday afternoon will not include the full evidence file of Connecticut State Police, which is believed to total thousands of pages. The decision to continue withholding the bulk of the evidence is stirring new criticism of the secrecy surrounding the investigation.

Dan Klau, a Hartford attorney who specializes in constitutional free speech law, said the decision to release a summary report before the full evidence file is a reversal of standard practice and one of the most unusual elements of the investigation.

"What I found troubling about the approach of the state's attorney is that from my perspective, he seems to have forgotten his job is to represent the state of Connecticut," Klau said. "His conduct in many instances has seemed more akin to an attorney in private practice representing Sandy Hook families."

Sedensky said he could not comment.

Twenty-year-old Adam Lanza killed his mother inside their Newtown home before driving to his former elementary school, where he fired off 154 shots with a Bushmaster .223-caliber rifle within five minutes. He killed himself with a handgun as police arrived.

Warrants released in March detailed an arsenal of weapons found inside the Lanza home. But authorities have not provided details on the police response to the shooting, any mental health records for Lanza and whether investigators found any clues to a possible motive for the rampage.

Sedensky has gone to court to fight release of the emergency call tapes from the school and resisted calls from Connecticut's governor to divulge more information sooner.

The withholding of emergency call recordings, which are routinely released in other cases, has been the subject of a legal battle between The Associated Press and Sedensky before the state's Freedom of Information Commission, which ruled in favor of the AP, and now Connecticut's court system. A hearing is scheduled Monday in New Britain Superior Court on whether the judge can hear the recordings as he considers an appeal.

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