Doering would not say how the eight were killed and would only say they ranged in age from teenagers to adults. A ninth victim was hospitalized Sunday in Savannah. Police are offering a $25,000 reward for information, with Doering saying, "We need help."
"The person or persons responsible for this still remain unknown to us," said Doering, who added the killer could have fled to another county or even another state. "I cannot tell you if they are at large. I simply do not know."
Police have arrested one man - a family member who lived in the mobile home and called 911 to report the attack, police said. Guy Heinze Jr., 22, faces charges of tampering with evidence, lying to police and illegal possession of prescription drugs and marijuana. He was jailed Sunday.
"He ... came home and discovered (the victims), at least that's what he told us," Doering said.
Asked if Heinze was involved in the slayings, Doering said: "I'm not going to rule him out, but I'm not going to characterize him as a suspect."
The killer was not among the dead or the last survivor, according to Doering.
Earlier, Doering said it the worst murder case ever in the county. Brunswick is a port city of about 16,000 people between Savannah and Jacksonville, Fla., along Georgia's east coast.
Police have released few details about the slayings in the mobile home on an old plantation, nestled among centuries-old, moss-draped oak trees in coastal southeast Georgia. Police have refused to say if the victims were related or give a possible motive.
The lack of information has frustrated residents, said Mary Strickland, who owns The Georgia Pig, a popular local barbecue place.
"I think a lot of people who live in that area would feel a lot better if they had a little more information," Strickland said. "If it is a murder-suicide then let people know so they don't think there's some lunatic out there. We got a lot of people who panic and the more information you put out there, the better you make them feel."
Doering defended his vague statements about the case, saying he didn't want the public to know details that might compromise what he called a "tedious" investigation.
The Georgia Bureau of Investigation conducting autopsies Sunday on four of the victims Sunday. GBI spokesman John Bankhead said Glynn County police would be in charge of releasing any results, and Doering refused to comment on them.
He said medical examiners would begin autopsies on the remaining four victims Monday.
Sandra Gause, who lives in another mobile home park about a mile from the crime scene, said she's been paying extra attention since the slayings to cars and people she doesn't know coming into her neighborhood.
"It just makes you wonder how safe your community really is," said Gause, 36, after buying a pack of cigarettes at a nearby convenience store. "What is going on? Two or three days later, we'd kind of like to know."
Associated Press Writer Dionne Walker in Atlanta contributed to this report.