NBC News adds one more piece to the puzzle: It reports that Adam Lanza had some kind of altercation with four staffers at Sandy Hook Elementary School on Thursday, the day before the massacre. Three of those staffers were killed, and the fourth was not at school yesterday and is being interviewed by police. It's not known what the dispute was about. NBC also says Lanza tried to buy a rifle at a sporting goods store but was unable to do so because of the state's waiting period. He was still well-armed when he arrived at the school, however, apparently with weapons registered to his mother, reports ABC News.