Police investigating the disappearance of a Hallandale Beach, Fla., boy last seen about 18 months ago have found remains that are consistent with an infant's, authorities said Friday.

Police Chief Dwayne Flournoy said it was too early to say whether the remains are those of Dontrell Melvin, who was 5 months old when he went missing around July 2011.

Flournoy said the missing person case has turned into a homicide investigation. Police are arranging for a specialist to further examine the remains, which were found in the backyard of a house where the parents once lived, in the 100 block of Northwest First Avenue in Hallandale Beach.

"We are investigating a homicide," Flournoy said. "Are the parents suspects? Yes." 

The arrests of Calvin Melvin Jr., 27, and Brittney Sierra, 21, were announced by police earlier Friday, before the remains were found. The parents were held on child neglect charges after they allegedly admitted they failed to provide adequate care for the child, Flournoy said.

Each parent implicated the other in the child's disappearance, and police soon after went to the Hallandale Beach site to conduct a search with cadaver-sniffing dogs, Flournoy said.

“After lengthy interviews over the last 12 hours, they both have intimated that the child has been harmed in some way by each other,” Flournoy said. “So in essence, they are blaming each other as it relates to the child’s disappearance.”

Little Boy Has Been Missing Since July 2011: Hallandale Beach Police

Dontrell’s disappearance didn’t become known to authorities until Wednesday, when an investigator with the Broward County sheriff’s Child Protective Investigations Section spoke to Sierra regarding a child neglect case, according to Hallandale Beach police Maj. Thomas Honan.

Instead of finding three children at the home, the CPIS investigator saw that Dontrell was missing, Honan said.

Sierra then contacted Melvin, who told the investigator that the boy was with Melvin’s parents in Pompano Beach, Fla., police said.

But when the investigator went to verify the story, the boy’s grandparents said they hadn’t seen the boy in more than a year, Honan said. The investigator notified Hallandale Beach police, Honan said.

Though police questioned Melvin and Sierra, neither has said what happened to the boy. Sierra told police that if the boy disappeared and was harmed, then Melvin did it, Flournoy said. Melvin said the same thing about Sierra: If the child was harmed, Sierra did it, Flournoy added.

The police chief said that the parents individually described “an area of interest and concern” where police could search to determine whether “the child has been harmed.”

“The evidence has led us to believe that their conspiracy -- to hide the whereabouts of the child after the child was missing -- is apparent,” Flournoy said.

Before the remains were found Friday, Flournoy said an area had been identified by the parents.

By Friday afternoon, Hallandale Beach police cruisers were parked outside a home where residents said the parents used to live.

Several officers were seen there searching the grounds. Assisting were Broward Sheriff’s Office crime-scene specialists, as well as Miramar police cadaver dogs, Flournoy said.

The current tenant of the home, Natalie Garrido, said her Labrador retriever used to dig in the same spot where the remains were found Friday.

“He would always go back there to sniff in that area. And he would disappear there," she said. "I’m like what is he smelling back there? Nothing was ever sketchy to me.”

Double Homicide of Elderly Couple in Hallandale Beach: Police

Melvin previously told police that he had dropped off Dontrell at a Miami Gardens fire station in 2011, but “he has since recanted that story,” Flournoy said. “He said that that’s not true.”

Thursday, Melvin provided a different account of events, police said. Before the boy vanished in 2011, Melvin said he had gotten into a verbal argument with Sierra and left the residence, Flournoy said.

Melvin said when he returned to the residence weeks later, Sierra told him the boy was living with her parents out of state, the police chief said.

Melvin said that when he pressed Sierra for answers at the time, Sierra asked for his forgiveness and told Melvin that if he loved her, he should no longer ask about the boy, Flournoy said.

Meanwhile, Sierra told police that Melvin had taken the boy away from the home in July 2011, police said.

After the disappearance, it was clear from questioning the parents that no family member had the child and that the parents knew of no one who had the child since either July 2011 or August 2011, police said.

Additional relatives of the boy likely didn’t investigate the boy’s disappearance because they were assured he was OK, police said.

“Perhaps the parents were able to spin stories to different segments of the family, that they believed the child was possibly being taken care of by another segment of the family,” Flournoy said. “But they never connected or talked.”

The police chief said relatives probably thought financial hardships had led to the boy being elsewhere. “The family believed that if someone else was providing for the child, that it was a better situation for the child to be in,” Flournoy said.

In October 2012, Melvin and Sierra had a child-custody issue that led Hallandale Beach police to notify the state Department of Children and Families.

The child-custody case stemmed from the mother making “the assertion that the father is keeping the child away from her and not allowing her to see the child,” Flournoy said.

Police at the time told DCF that the family was having a child-custody issue and said they may require their services.

DCF Secretary David Wilkins said in a statement on Friday that DCF had last year “worked with the officer at that time regarding the police department’s ongoing investigation into a custody dispute between the two parents arrested today.”

Wilkins said DCF couldn’t discuss specifics, but replied that “’missing child cases and situations where a crime is alleged to have occurred remain under the investigatory authority of local law enforcement.”

DCF is working “very closely” with Hallandale Beach police and the Sheriff’s Office in the inquiry, Wilkins added.

Dontrell’s two siblings now are in the custody of DCF, Wilkins said. “We are providing them with the safety and security they need,” he said.

The boy's parents were taken to a Broward County jail on Friday and were expected to make their first court appearances as early as Saturday, Flournoy said.