No charges had been filed as of Saturday morning against a 26-year-old woman considered a "person of interest" in the slaying of 23-year-old Jimella Tunstall, whose body was found Thursday.
Tunstall's children — ages 7, 2 and 1 — were last seen Monday with the woman now detained, authorities said Friday, clinging to hope that the youngsters still would be found alive.
"These children are from East St. Louis," said Police Chief James Mister. "They know how to survive."
The Associated Press is not naming the woman in custody because she has not been charged with any crime.
Relatives of both women told media outlets the two grew up together and attended alternative schools. The woman in custody often baby-sat Tunstall's children, and Tunstall never expressed worry about leaving them in her care, the St. Louis Post-Dispatch reported.
Saturday's search came a day after a meticulous scouring of the 1,100-acre Frank Holten State Park, just blocks from where Tunstall's body was found. Investigators would not say what led them to believe the children were there.
"Our main concern at this point is trying to find the children alive," State Police Capt. Craig Koehler said.
Investigators told CBS affiliate KMOV-TV in St. Louis that the baby was most likely cut from the victim's womb last week.
"We're continuing to conduct our murder investigation and we are considering the death a murder," Koehler said.
Ace Hart, a deputy St. Clair County coroner, said the woman in custody summoned police to the Frank Holten park on Sept. 15, saying she had gone into labor. The dead baby, taken to a hospital, showed no signs of trauma, and an autopsy the next day failed to pinpoint a cause of death, he said.
The woman would not let doctors at the hospital examine her and offered conflicting reasons for why she went into labor, alternately saying she had consensual sex and was raped, Hart said.
Authorities say the woman in custody acknowledged to her boyfriend during the baby's funeral Thursday that the child wasn't his, and that she killed the mother. The boyfriend told police, who arrested his girlfriend hours later, investigators said.
An autopsy Friday showed that Tunstall died of an abdominal wound caused by a sharp object, and "we're thinking it's scissors" found near the body, Hart said.
The slaying was "very graphic and very brutal," he said. The body was found in a lot not far from the home of the woman in custody.
DNA tests should determine definitively whether the baby was the one Tunstall was carrying, Hart said.
Authorities have refused to discuss many details of the case, including whether the two women knew each other, where the person of interest was being held or if she had an attorney. Also unclear was which came first: the discovery of Tunstall's body Thursday or the alleged funeral confession by the woman in custody.
The baby was buried Thursday as Taylor Horn after a funeral arranged by L. King Funeral Chapel, whose president said the 26-year-old who claimed to be the mother called minutes after the service was to start, asking if she could reschedule for a different day so more relatives could attend. At the time, Levi King said, only two relatives were there.
The woman showed up two hours late, ultimately signing an affidavit for the funeral home stating that the child was hers, King said.
The 26-year-old woman had been taken to the hospital the same day a young mother's throat was slashed and her baby kidnapped in Lonedell, Mo., south of St. Louis. An arrest has been made in that case, the mother is recovering and the baby was returned unharmed.
Also in Missouri, Lisa Montgomery will stand trial April 30 on charges of snatching a baby from the womb of Bobbie Jo Stinnett at her Skidmore, Mo., home in 2004. The baby survived.