Adam Lanza, who massacred 26 people at an elementary school in Newtown, Connecticut, committed suicide as soon as he heard police approaching, indicating that he may have planned an even larger massacre, Connecticut Gov. Dan Malloy said Sunday on "This Week" on ABC.

Investigators have not revealed what the possible motive for the massacre at Sandy Hook Elementary School may have been, but the 20-year-old Lanza may have been looking to kill even more people.

"We surmise that it was during the second classroom episode that he heard responders coming and apparently at that decided to take his own life," Malloy said.

Police have not found any letters or diaries that shed light on why Lanza committed the massacre, the governor said.

"I think our nation needs to take a very different approach to mental health, and we need to speak about it more honestly, just as we need to do other things," Malloy said.

Lanza used a .223-caliber assault rifle and was carrying two handguns.

All of the victims - six adults and 20 children - were shot at least three times, Connecticut state medical examiner Wayne Carver said Saturday.

Lanza's weapons were all owned by his mother, Nancy, who he killed before setting off for the school.

President Barack Obama plans to visit Newtown on Sunday afternoon to express his condolences to the families of the victims. EFE