Flournoy said he was never made aware that DCF had declined to investigate the call. “I’ve been told that something did happen with that October hotline call,” he said. “I’ve been told there was some response.”

Follick confirmed that DCF “had a number of instances of involvement with this family in recent years,” but would not elaborate. The Miami Herald has learned that privately run child welfare agencies under contract with the state had been working with members of Sierra’s extended family as recently as last year, and that DCF had removed children from the home of Sierra’s mother — with whom the couple had been living most recently.

“We continue to work very closely with the Hallandale Beach Police Department and the Broward County Sheriff’s Office on this investigation,” Follick said. “The death or disappearance of any child is a terrible tragedy that saddens every member of the community and every employee of this department.”

Flournoy said investigators were led to the couple’s former backyard after interviewing Melvin and Sierra.

The home is now occupied by Mahud Lama. Police told him to stay clear of the backyard while they investigated. Cadaver dogs were summoned and indicated someone could be buried there. Broward Sheriff’s Office deputies probed the area with metal spikes. An area of soft dirt was found, and the bones were located underneath. A medical examiner confirmed the remains were human.

Melvin, who reemerged Thursday night after disappearing from his current home earlier, offered police a variety of stories about his son’s disappearance. One was that he had left the boy at a North Miami-Dade fire station — which is legal under the state’s Safe Haven law, though only for about a week after a child’s birth.

Police didn’t believe him.

Sierra initially told police that Melvin walked out of their Hallandale Beach home with Dontrell in July 2011 — and came back without him. When she pressed Melvin about what he had done with the boy, he said he had given the child to his parents. She said she believed him, and life went on in the Hallandale Beach house, minus Dontrell.

Melvin and Sierra would have another child. There was also a third child — one by a different father — in the household.

Throughout the coming months, no one — not Sierra, not Melvin, not the boy’s grandparents nor other family members — reported to authorities that Dontrell had vanished.

“That’s what’s confusing,” the police chief said. “This is a large family unit — with grandparents and uncles and aunts — and everyone just thinks this child is with another segment of the family. We know the mother and father had problems, including financial problems. But nobody circled back and checked” on the child’s safety.

About a year ago, the family left the little green house and moved in with Sierra’s mother, just six blocks away.

Rosetta Braham, who lives next door to Sierra’s mother, said there were now six youngsters living there — two of them Sierra’s children. But she never saw Dontrell, never knew he existed.

Last August, Braham said, she took Sierra’s mother shopping for backpacks for her children and grandchildren. “She told me she had a dream that her grandbaby was missing,” Braham said. What neighbors did see were frequent arguments between Melvin and Sierra, some of which spilled into the front yard.

The two would “fuss and fight a lot,” Braham said, and Melvin would come next door and sit on her porch.

But Sierra would eventually come over, and the couple would reconcile.