According to a report issued Thursday, police think the 15-year-old suspect started last week's shooting spree by killing his elder brother.
Raleigh's police chief sent the city manager a four-page report on the shootings. Five business days after an officer-involved shooting, these summaries are prepared.
Police said an off-duty municipal police officer was among those killed in the Oct. 13 killings in Hedingham.
Two people were injured, including a resident who is in critical but stable condition.
Witnesses said a gunman in camouflage fired a shotgun in the neighborhood and along a nearby path.
Police said the culprit, still unnamed in the report since he's a child, was arrested in a barnlike facility four hours after the initial emergency call.