All of those killed by the gunman, identified as Joseph Aldridge, 36, lived within a few miles of each other in the tiny community of Tyrone, an unincorporated area with a population of about 50, authorities said.
Authorities said the motive was unclear and declined to comment on whether the murders had been triggered by the death of Aldridge's mother, who was found at her home. Authorities said she may have died from natural causes.
"It's heartbreaking," said Todd Haley, senior pastor at Ozark Baptist Church, about three miles from Tyrone. "Anytime you see families that go to this level of violence, it's a shame."