Harrison County Prosecutor Jack Shaffer said a drug deal went wrong around 4:30 a.m. Friday in a neighborhood known for drug activity.
Shaffer would not say if a suspect is in custody. Shaffer instead said investigators expect no more activity from the individual responsible and the public is not in danger.
Police are not identifying any of those killed. Shaffer said the two bystanders worked a job that had them in that area at that time each morning.
A lifelong Harrison County resident, Shaffer could not recall an event in his area with so many victims.
Investigators were expected to release more details Friday.