An autopsy on a newborn girl whose decomposing body was found Tuesday in a plastic garbage bag beneath her mother's bed appears to confirm that the child was born alive, then died as a result of a stab wound to the neck.

Investigators said the cause and manner of death won't be final until toxicology reports are finished within the next few days. Preliminary indications are that the baby lived for a brief period after her birth Feb. 28 between 10 p.m. and midnight.

The baby's mother, Lauren Elizabeth Jones, 24, of Buffalo Township, Butler County, has been charged with homicide, concealing the death of a child, endangering the welfare of a child and abuse of a corpse. She was held without bond in the Butler County Jail.

The baby's body was found Tuesday evening when the child's grandmother asked a visiting friend to investigate an odor coming from beneath her daughter's bed. Ms. Jones has been living on Monroe Road with her mother and stepfather, Debra and Joseph Troutman, since December. Mrs. Troutman couldn't check under the bed herself due to a medical condition that restricts her movement so she asked her friend for assistance.

What they found was the decomposing body of a baby inside a black, plastic garbage bag that was stuffed into a backpack, according to a criminal complaint.

Mrs. Troutman told police she had asked her daughter whether she was pregnant several times since December but that her daughter had denied it. She said she did not know her daughter had given birth Feb. 28 and hadn't seen Ms. Jones since she had left home Sunday morning with her 14-month-old son. She was contacted by police at the home of her boyfriend in Pittsburgh early Wednesday.

During a police interview, according to the complaint, she told police she went into labor a week earlier in the basement of her home, outside Sarver, and that the baby was born with the umbilical cord wrapped around her neck. She said she couldn't detect a pulse or a heartbeat. She said she couldn't ask her parents, who were upstairs, for help because she "couldn't physically make it up the steps."

Police said that after she was told that an autopsy would be conducted on the baby, Ms. Jones said "that the only thing that she did so that the baby wouldn't suffer was to stab it [in the neck]." She said she did it with a steak knife she obtained from the upstairs kitchen after the birth.

"The defendant admitted that the baby did move once prior to stabbing it but she doesn't know if this was just its muscles moving or because of the birth,'' the complaint reads.

She told police she didn't know she was pregnant until she went into labor.

Butler County Deputy Coroner Larry Barr said he expects to have toxicology reports complete by Monday. He said the autopsy showed the baby was full-term and had a puncture wound to the throat.