SEATTLE — The US soldier accused of carrying out one of the worst atrocities of the Iraq and Afghanistan wars is due to appear in a military courtroom Monday, where prosecutors will for the first time lay out their case that he slaughtered 16 people, including children, during a predawn raid on two villages in the Taliban’s heartland.

Staff Sergeant Robert Bales, a married father of two from Lake Tapps, Wash., is accused of slipping away from a remote outpost in southern Afghanistan early on March 11 with an M-4 rifle outfitted with a grenade launcher to attack the villages of Balandi and Alkozai, in the dangerous Panjwai district of Kandahar Province.