Three young children who police found unresponsive early Monday on the beach at New York's Coney Island all died by drowning, the city's Office of Chief Medical Examiner said Tuesday.
The manner of each of their deaths was ruled a homicide, the office determined.
Police detained the children's mother, who is suspected of drowning them, authorities said.
The medical examiner's findings will advance the investigation and help determine whether the mother, who remains hospitalized for evaluation, should be charged, officials said.
The grim discovery came at 4:42 a.m., about 90 minutes after police launched a frantic search for the children, whose 30-year-old mother was found soaking wet, barefoot and uncommunicative on the Coney Island Boardwalk, police officials said during a news conference. One official briefed on the probe told ABC News that the mother was "nearly catatonic” when police attempted to speak with her Monday morning.
Detectives are looking into whether postpartum depression played a role in the triple slaying, the official said.
Kenneth Corey, chief of department for the New York Police Department, said officers immediately performed cardiopulmonary resuscitation on the children, who were taken to Coney Island Hospital, where they were all pronounced dead. While autopsies will be conducted to determine the cause of death, police suspect the children died from drowning, officials said.
Corey described the children as a 7-year-old boy, a 4-year-old girl and a 3-month-old boy. Their names were not immediately released.
Corey said the incident unfolded around 1:40 a.m., when a relative called 911 and said she was concerned that the mother was going to harm the children.
"I believe she (the mother) had called them and made statements to that effect," Corey said.
Officers went to the mother's apartment in Coney Island, knocked on the door but got no answer, Corey said. While at the address, a man showed up and identified himself as the father of one of the children, who also expressed concern for the well-being of the children and told officers he believed the mother had taken them to the boardwalk.
Corey said police immediately launched a search of the mother's apartment, which was unlocked, the boardwalk, the surrounding neighborhood and the beach. They found the mother on the boardwalk with other relatives, but her children were nowhere in sight.
"She was soaking wet, she was barefoot and she was not communicative to the officers," Corey said.
He said the search for the children intensified with NYPD helicopters and boats being deployed.
Corey said the children were found unresponsive at the water's edge near the boardwalk at W. 35th Street.
He said the mother was found about two miles from where police discovered her children.
Police said the deaths of the children appear to be premeditated and not something that occurred at the spur of a moment. Detectives are looking into the mother's past and interviewing neighbors and relatives, officials said.
The mother has no prior arrests or history of being emotionally disturbed, according to NYPD records. She has prior domestic incidents of harassment and aggravated harassment that did not result in charges, according to the records.
"Best we can tell at this point, and again it's preliminary, there is no indication of a prior history of abuse and neglect of these children," Corey said.
Corey said the mother, whose name was not released, was detained for questioning, but has not been charged.
While police said they are investigating whether postpartum depression played a role in the episode, Dr. Anna Yegiants, a resident physician and member of the ABC News Medical Unit, explained there is a difference between postpartum depression and postpartum psychosis.
Yegiants said that while it is possible for someone with postpartum depression to harm their children, it is not common. She said postpartum psychosis, however, presents essentially a break with reality and causes delusional thinking that could lead to such violence.
Up to 1 in 7 women experience postpartum depression, according to the American Psychological Association, and symptoms can occur during pregnancy and last for days or even months after delivering a baby.
"Postpartum depression is not your fault -- it is a real, but treatable, psychological disorder," the APA says on its website. "If you are having thoughts of hurting yourself or your baby, take action now: Put the baby in a safe place, like a crib. Call a friend or family member for help if you need to."