The heartbreaking details in the case of Dontrell Melvin have begun to emerge. The missing boy’s parents have been arrested on child neglect charges, police have unearthed a small skeleton from behind a home they previously rented and investigators are checking DNA to determine whether the bones are those of the child.

It seems clear that something awful has happened to Dontrell. That’s up to police to determine, and punishment for those involved will be determined by the courts. But there’s another question that a civilized society must also answer: How does a five-month-old baby go missing for 15 months and no one look for him?

The explanations so far have been tissue-paper thin. There were four calls to the state’s abuse hotline since March 2011 that could have alerted authorities to something wrong in Dontrell’s household. Of the four, the hardest to explain is the call in October from a Hallandale police officer who said the boy hadn’t been seen in more than a year and the mother wasn’t sure if “the baby is even alive or not.”

The state Department of Children and Families — despite some 30 prior hotline calls involving Dontrell’s extended family — categorized that call as a missing child report that should be investigated by law enforcement. Hallandale police, meanwhile, apparently thought DCF would take any needed action.

It wasn’t until the fourth call to the hotline — this one from a neighbor, in January — that the boy’s disappearance came to light last week. A few days later, investigators unearthed the remains.

To be fair, no one knows whether speedy intervention by DCF or police could have averted a tragedy. But when a police officer calls about an infant missing for 15 months and the family is already well known to DCF because of dozens of calls to the abuse hotline (the content of the calls has not been made public), any reasonable investigator should have insisted on laying eyes on all three of Britney Sierra’s children.

And for the Hallandale police to assume the hand-off to DCF was complete after a single phone call is another abdication of responsibility. Surely both agencies owed that child a second phone call, a follow up interview, some sort of extra effort. If a missing infant doesn’t set off the alarm bell for public safety and child welfare officials, what does?

We already have a long, sad history of missing children in South Florida. This case comes less than two years after the death of Nubia Barahona, a 10-year-old whose adoptive parents are accused of killing her, and more than a decade after the disappearance of 4-year-old Rilya Wilson, who prosecutors say was killed by her caregiver. In both prior cases, a task force urged greater urgency on missing child reports. Lawmakers pumped millions of dollars into the technology and training for the Florida Abuse hotline just last year.

But we’ve failed again. Now, instead of ducking responsibility, DCF must find out what went wrong, work better with law enforcement officers and give this child the justice he deserves.