Police in the US state of Colorado say a woman stabbed a pregnant mother in the stomach and took her unborn child.
The victim, who was seven months pregnant, is likely to survive following surgery, but the baby died.
The pregnant woman was visiting the suspect's home to buy baby clothes that had been advertised on the online marketplace Craigslist.
The suspect, Dynel Catrece Lane, lost a 19-month-old child over a decade ago when he drowned in a small fish pond.
The 26-year-old expectant mother was responding to an online advertisement for baby clothes when the attack occurred on Wednesday.
"When she got into the house, she was attacked, she was beaten, and her baby was removed or cut out of her," Longmont Police Cdr Jeff Satur said.
The victim was able to make an emergency call, but was said to be barely conscious when officers arrived.
"She cut me," the woman says with a dazed-sounding voice in a recording of the emergency call. "I'm pregnant."
By the time officers arrived to assist the victim, Ms Lane had already left the scene.
Police say the 34-year-old suspect told her husband, David Ridley, that she had experienced a miscarriage. He rushed her and the baby to the hospital.
Ms Lane has two children of her own, and she and her husband had been trying for another.
She did not know the victim, police said.
The Longmont Times-Call newspaper said the arrest report suggested that Ms Lane was pregnant herself, and she had admitted to cutting the baby out of the victim.
Police have arrested Ms Lane on suspicion of first-degree murder, first-degree assault, and child abuse knowingly and recklessly resulting in death.
The timing of the unborn child's death is complicating the process of filing charges against her.
Boulder County District Attorney Stan Garnett is reportedly trying to determine if the child was still alive when it was removed from the womb.
"Under Colorado law, essentially no murder charges can be brought if the child did not live outside of the mother," the local paper quotes him as saying.
Mr Ridley told police that he saw and heard the baby take a "gasping breath", according to the arrest report reviewed by the Times-Call newspaper.
An autopsy has been scheduled for Friday.
The mother is said to be alert and responding to police questions.
Authorities are now looking for any other mothers who may have responded to the advertisement posted on Craigslist.