Three youngsters found wounded but alive in a house where six other people were slain are under police protection, and not even their relatives can visit them in the hospital, police said.
Authorities consider the children as witnesses.
"Nobody will see those children," said homicide detective Joe Scott. "This is a sensitive investigation. We're keeping everything under the wraps right now."
Police offered no motive for the killings, which occurred over the weekend at a small brick house in a neighborhood where low-income homes sit near cheap motels and junkyards.
Authorities identified the adult victims Wednesday as Cecil Dotson, 30, who was renting the house; Hollis Seals, 33; Shindri Roberson, 20, and Marissa Rene Williams, 26. They declined to identify the children.
Police put the time of the killings somewhere between Saturday night and Monday evening. Five of those killed were shot and at least one, a child, was stabbed, authorities said. Investigators have ruled out a murder-suicide.
Dotson's sister, Nicole Dotson, said her brother lived in the rental house with Williams, his girlfriend, their four children and a child of his from a previous relationship. The children were ages 9, 5, 4, 2 and 2 months, she said.
Police refused to disclose any information about the surviving children, even to their relatives.
"We don't know who's in the hospital. We don't know who's alive. It's depressing," Dotson said.
No one called police
Residents near the murder scene said gunfire is not unusual in their neighborhood, and no one called police when shots were heard over the weekend.
"I did hear shooting, but I didn't know where it was. Sometimes guys get crazy and just shoot up in the air," said Marie Mackey, 33, who was visiting her mother's house a couple of blocks away Saturday night. "If I had known, I would have called."
Billy E. Gunn, whose house is behind the home where the bodies were found, said he heard five rapid gunshots and then three slow ones around 9 p.m. Sunday. He said he didn't call police because it's such a common sound.
"It wouldn't have mattered; it takes the police so long to get out here," he said.
Ricky Hall, 52, who lives near the home where the bodies were found, says the neighborhood has grown more unkempt and dangerous in the past few years, with many rental homes sitting empty.
Investigators say they have few leads to work with. The Memphis City Council announced a $30,000 reward Wednesday for anyone who can help solve the case.
Police refuse to say if the slayings could be connected to Dotson's violent past.
Criminal histories surface
Court and criminal records reviewed by The Associated Press showed Dotson was "known to have gang affiliations" when he joined in an attack on a prison farm inmate in 1995 while serving a four-year sentence for aggravated assault.
At the time Dotson died, a charge of aggravated robbery was pending against him. An affidavit filed by police accused him of driving a van that nearly struck a pedestrian on Jan. 9. When the pedestrian approached the van and yelled, Dotson pulled out a handgun and demanded the man's wallet. Dotson was arrested shortly afterward and identified by the victim.
The other dead adults also have arrest records. Seals was booked into the Shelby County Jail at least a dozen times since 1992. His last arrest was last month, on charges that included unlawful possession of a weapon and cocaine possession, the sheriff's department said.
Roberson had an arrest record on prostitution and drug charges, while Williams had an arrest record for traffic violations, said sheriff's spokesman Steve Shular.