When authorities arrived Saturday morning, they found seven people dead and two clinging to life. One of the survivors died Sunday, raising the death toll to eight.
Police have refused to say how they were killed or why and have said they don't know if the attacker is still in the area. Police have not identified a suspect and are offering a $25,000 reward for information.
"We still believe there is a person or persons responsible for this somewhere out there, and we're looking for them," Glynn County Police Chief Matt Doering said Monday.
Heinze, who spoke with the 911 operator from a neighbor's house, was later arrested on drug and other charges, including lying to police.
Asked if Heinze was involved in the slayings, Doering said Sunday: "I'm not going to rule him out, but I'm not going to characterize him as a suspect."
On the 911 call, Heinze said his father, uncle and cousins were among the dead. After handing off the phone to an employee at the mobile home park, Heinze apparently returns to the trailer and is overheard on the call screaming that his cousin Michael, who had Down syndrome, was still breathing and that his face was "smashed in."
"Michael's alive, tell them to hurry!" Heinze said, in the background. "He's breathing! He needs help!"
Police on Sunday said one person rescued at the scene, 19-year-old Michael Toler, had died at a Savannah hospital. The only survivor, whose name and age has not been released, remains in critical condition.
Police have said the attacker was not among the dead or the last survivor. They also said they have no evidence to suggest suicide was involved.
Neighbor Margaret Orlinski, who called 911 after Heinze came screaming to her home, told a 911 operator that a baby also lived in the mobile home where the victims were found.
"I know there's a little baby," Orlinski says on the recording. "Shoot, there's a little babe. I don't know if the baby was in there or not."
Heinze doesn't mention a baby on the 911 recording. Police have declined to give ages of the victims, but Doering has said there were "no infants" among them.
Police have urged residents to be aware and cautious, and the uncertainty has created fear among some in the town.
Resident Toni Mugavin said she wonders if she needs to sleep with a gun under her pillow, afraid the killer is still on the loose. Mugavin expressed frustration with the lack of information about what happened.
"There's no manhunt, no suspect," said Mugavin, 50. "There's nothing specific they're telling us."
Earlier, Doering said it was the worst murder case he had ever encountered in his 25 years with the county that includes Brunswick, a city of about 16,000 people between Savannah and Jacksonville, Fla., along Georgia's southeastern coast.
The slayings happened in a mobile home park on the grounds of a historic plantation, nestled among centuries-old, moss-draped oak trees. The park consists of about 100 spaces and is near the center of New Hope Plantation, according to the plantation's Web site.
The 1,100-acre tract is all that remains of a Crown grant made in 1763 to Henry Laurens, who later succeeded John Hancock as president of the Continental Congress in 1777.
The Georgia Bureau of Investigation was conducting the autopsies. GBI spokesman John Bankhead said Glynn County police would be in charge of releasing any results, and Doering refused to comment on them.
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.
Still, the dearth of information has frustrated residents, said Mary Strickland, who owns The Georgia Pig, a popular local barbecue place.
"We got a lot of people who panic and the more information you put out there, the better you make them feel," Strickland said
Associated Press Writer Dionne Walker in Atlanta contributed to this report.