The gunman in the Newtown massacre had an “altercation” with four staff members at Sandy Hook Elementary School the day before he killed 20 children, six adults and himself there, Connecticut and federal officials told NBC News Saturday.

Three of the four staff members were killed Friday in one of the worst school shootings in U.S. history. The fourth staff member was not at school that day and is being interviewed by federal and state investigators, NBC News’ Pete Williams said.

Two days before that, Adam Lanza, 20, went to a sporting goods store in Danbury, Conn., and tried to purchase a rifle, but was rebuffed because the state has a waiting period for gun sales, the officials said.