(CNN) -- The search for a 3-year-old Alabama boy began just weeks ago, but police now say that no one had seen him since March -- around when, they believe, he was killed by one or two of his parents.
John Joseph DeBlase, Heather Keaton and Natalie -- the father, stepmother and 4-year-old sister, respectively, of Jonathan DeBlase -- continued to live in Mobile's Peach Place apartments for months after the boy's presumed death, Mobile police Officer Christopher Levy said Monday.
They didn't leave until the summer, after Natalie was last spotted in June -- when police now think she was killed, according to Levy. Still, the search for the two children, whose bodies haven't been found, didn't begin until November 19.
"It's really terrible, as if nobody really cared," Levy said of the time that transpired between the sightings and launch of the search. "That's what we can't seem to understand at this point."
Both John DeBlase and Keaton are now in custody, and blaming each other for the siblings' deaths. The search for their bodies, meanwhile, continues.
Mobile Police Chief Micheal T. Williams told HLN's Nancy Grace on Monday that the father "gave us an indication of where the two children buried," leading to searches for their bodies at two locations over the weekend.
"Our hearts are broken, because these two beautiful children are missing and presumed to be dead," Williams said. "We will continue our searches until we locate the bodies and they are properly buried."
This weekend, authorities started looking in a rural 12-mile swath in southeastern Mississippi, about one hour's drive from Mobile.
"They think that somehow, maybe, one of the children may have been brought here and dumped," said Jackson County, Mississippi, Sheriff Mike Byrd. "But we're not really sure where to look."
Byrd said that he believes that John DeBlase wanted to bury one of the children with a shovel, but tossed the body instead because the ground was too hard. Searchers, some with cadaver dogs, have looked on the sides of nearby roads and in a wooded area.
Police have also searched for the children's bodies in Citronelle, about 33 miles north of Mobile, according to CNN affiliate WKRG.
The investigation kicked off November 18, when Keaton told Louisville, Kentucky, police that she needed protection from DeBlase, who she claimed was "holding (her) against my will."
According to the domestic violence petition, signed Heather L. Leavell-Keaton, she said, "I feel he may have murdered his children, because he said they were non-responsive. He would not let me check on them." She said John DeBlase had told her "choices were made ... and he had to do what he had to do."
Keaton herself was arrested last Tuesday, charged with two counts of willful abuse and neglect of a child.
Three days later, Randall Melville -- who for two days had been hosting his long-time friend, John DeBlase -- called Santa Rosa County, Florida, police after hearing news reports about the children's disappearance, according to a report from the county sheriff's department.
When Melville asked DeBlase about it, the children's father yelled, "I didn't do it" and left the home, the report said. Police eventually tracked down John DeBlase, who again asserted his innocence before his arrest Friday.
He faces two counts of aggravated child abuse and two counts of abuse of a corpse -- the latter because, Levy said, of his "disposing of the bodies in the woods."
On Monday, Mobile County District Court Judge Charles McKnight set bail for DeBlase at $206,000 -- $100,000 each for the child abuse charges, and $3,000 apiece for the corpse abuse counts -- reported CNN affiliate WALA.
Prosecutors had asked for no bail, given the severity of the crime and saying DeBlase was a flight risk given that he stayed in homeless shelters to avoid being caught.
John DeBlase and Keaton had one infant daughter together, according to Keaton's account in the Kentucky police report. Police said one reason Keaton claimed she needed protection from DeBlase was that she feared for the safety of the infant, who was with Keaton in Kentucky.
Levy said the two slain children's biological mother lives in Mobile, but she did not have custody "because, at the time, she didn't have a place to live."
People in and around Mobile, meanwhile, are mourning the loss of the two youngsters.
"We're just heartbroken," said Creighton Hobbes, a family friend. "We miss them. We want to see their little faces... We wanted them back around Christmas."
CNN's Andy Rose and Natisha Lance contributed to this report.