Grandmother, 3 grandchildren found shot, killed in North Dakota NEW TOWN, N.D. - A northwestern North Dakota home teemed with FBI investigators Monday as they tried to piece together evidence in the grisly weekend shooting deaths of a woman and three of her grandchildren. In a nearby community, a man described only as a "person of interest" in the killings apparently killed himself just hours after their deaths. This is a nice little quiet town. Now this is happening. Maddie Mendoza, a nearby resident Martha Johnson, 64, and three of her grandchildren -- Benjamin Schuster, 13, Julia Schuster, 10 and Luke Schuster, 6 -- were gunned down in the home Sunday afternoon, Mountrail County Sheriff Ken Halvorson said. Johnson's husband was out hunting. A fourth grandchild, a 12-year-old boy, was in the home but wasn't hurt and called 911, the sheriff said. "Person of interest" kills self with knife in front of deputies hours after their deaths The killings apparently occurred when Martha Johnson's husband was out hunting Small community has fewer than 2,0000 residents New Town is on an American Indian reservation called Fort Berthold. The suicide that followed occurred in Parshall, a reservation community about 20 miles from New Town. The man, in his 20s, killed himself with a knife in front of a deputy and a highway patrolman, Halvorson said. Authorities declined to identify the "person of interest," but did say he was an enrolled tribal member. Neither Johnson nor her grandchildren were members, Halvorson said. The FBI is leading the investigation into the deaths because the federal government has jurisdiction over crimes on reservations. FBI spokesman Kyle Loven declined to release details, citing the ongoing investigation. He said late Monday that the name of the man who killed himself and what role -- if any -- he played in the deaths would not be released until authorities pieced together what happened. Both Halvorson and the FBI said they didn't think there was any danger to the public, but New Town, a community of fewer than 2,000 residents, remained on edge Monday. Slayings are relatively rare in North Dakota, which is home to fewer than 700,000 people. FBI statistics show that in 2011, only 24 murders and non-negligent manslaughters occurred. Megan Hale, 22, lives across the street from the Johnsons' home. She said that the youngsters seemed to have moved in with Martha and Harley Johnson recently. She never saw the children's mother, whom authorities declined to identify. Hale knew Martha Johnson as a friendly neighbor. She was a nice lady. She was always out in the yard working," she said. It's unreal. Hale never heard the gunfire that apparently took the four lives, only learning of the tragedy when police arrived Sunday, she said. After that, the usually quiet street was blocked off for nearly 12 hours as investigators gathered evidence. On Monday, there was a teddy bear holding a note with a heart painted on it stuffed in the white picket fence that surrounds the Johnsons' beige-colored ranch-style home, which sits on a corner lot. The local school cancelled classes, and the community planned to hold a nighttime prayer vigil. The home is about 150 yards from an elementary school. FBI agents were in the home Monday, while crime-scene cleaners in white coveralls and breathing masks worked into the evening. Tex Hall, the Three Affiliated Tribes chairman, called the killings the "worst tragedy" to happen on the reservation that he could remember. "It's a terrible loss, especially when young kids are involved," he said. It's a sad, sad day. Newcomer Maddie Mendoza, a 21-year-old coffee shop worker who moved from Arizona in August, said everyone she has talked to is shocked and saddened by the killings. "This is a nice little quiet town," Mendoza said. Click for more from the Minot Daily News