Connecticut's chief state's attorney by March 29 will release new information regarding the investigation of the deadly shooting at Sandy Hook Elementary School, Gov. Dannel Malloy announced Thursday.

The move comes after a string of recent articles based on leaks detailed the gunman's planning before the attacks.

"Like many others, I was disappointed and angered to learn that certain information about the Newtown shooting had been leaked," Mr. Malloy said in a news release, referring specifically to concerns for the feelings of victims' families.

On Monday, the New York Daily News reported that investigators found a seven- by four-foot spreadsheet that belonged to Sandy Hook gunman Adam Lanza that contained extensive research about mass murders. The account was said to be based on information from an unnamed law-enforcement officer who attended a police conference last week in New Orleans, where Col. Danny Stebbins of the Connecticut State Police spoke about the investigation.

Mr. Malloy said he contacted the office of the chief state's attorney Thursday and asked that additional information on the investigation be released. What new details will be included will be determined by the state's attorney and other law-enforcement authorities, he said.