An odor coming from beneath a bed in Butler County led to the discovery Tuesday of a dead baby girl and the arrest of her mother.

Lauren Elizabeth Jones, 24, was charged with homicide, concealing the death of a child, endangering the welfare of a child and abuse of a corpse. She was held in the Butler County Jail without bond.

"We're just all messed up right now," Ms. Jones' stepfather, Joseph Troutman, said yesterday, sobbing.

Butler County District Attorney Randa Clark said Ms. Jones' mother, Debra Troutman, had noticed a foul odor coming from her daughter's room but, because of recent surgery, was unable to lower herself to the floor to investigate. At about 4:45 p.m. Tuesday, she asked a visiting friend to check under the bed in the home on Monroe Street in Buffalo Township, just outside Sarver.

"They found a black plastic garbage bag and, in it, the body of a newborn baby girl,'' said Ms. Clark. The infant was inside a backpack in the garbage bag.

At the time, Ms. Jones was visiting her boyfriend, Samuel Jackson, who lives in Pittsburgh. Ms. Jones has identified Mr. Jackson as the father of the dead baby.

Ms. Jones also has a 14-month-old who is in the custody of the child's father, also a resident of Pittsburgh.

She told police she gave birth Feb. 28 between 10 p.m. and midnight at the home she shared with her mother and stepfather.

According to an affidavit obtained by KDKA-TV, Ms. Jones told police that the umbilical cord was wrapped around the baby's neck. She said she stabbed the baby in the throat to end its suffering. The affidavit says Ms. Jones told police the baby moved once before she stabbed it.

Ms. Clark said she could not be specific about the baby's age at the time of death or the cause of death. An autopsy was to be performed last night.

She said Mrs. Troutman had been unaware that her daughter gave birth last week.