WEST BRANCH, Iowa — A distraught Brianna Marshall told an emergency dispatcher that she found a knife by her bed and that she didn't believe her half-sister had abducted her newborn in a 911 recording released Monday.

Marshall, 18, dialed 911 from a residence in Beloit, Wis., at 4:34 a.m. Thursday morning after awaking to find her infant son, Kayden Powell, missing from the bassinet by her bed.

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Authorities released to Wisconsin media the nine-minute 911 recording Monday, three days after West Branch (Iowa) Police Chief Mike Horihan found the baby wrapped in blankets in a plastic crate outside a gas station. Marshall's half-sister, 31-year-old Kristen R. Smith, was arrested in West Branch last week and faces federal kidnapping charges, once extradited.

Marshall, sobbing in the early morning call, told the dispatcher that she had already spoken with her sister on the phone before she dialed 911. Marshall insisted Smith, who had left the house in the middle of the night to return home to Colorado, didn't have the baby.

"I called her and she's bawling her eyes out and told me to call the cops," Marshall said of her half-sister.

"OK, but she's claiming she doesn't have the kid, correct?" the dispatcher asked.

"No, she wouldn't take my son."

"Is she going to be turning around and coming back to the house?"

"Most likely."

Marshall told the dispatcher that she put the baby down to sleep at 1:30 a.m. in a bassinet. She said that only she, her boyfriend, her grandmother and uncle were at home, though her sister had been there earlier in the night.

When Marshall awoke, there was a knife laying by her bed and the bassinet was empty, she told the dispatcher.

"I picked it up and seen it was a knife, and I threw it back down and looked over and my baby was gone," Marshall said. "Can you just please have the police here?"

Marshall handed the phone to a woman who was apparently her grandmother, who did not identify herself. The dispatcher asked the grandmother if Smith — whom the grandmother said was newly married and heading back home to Colorado — had anyone else with her.

"No, she was by herself," the grandmother said. "She's been down here for two days."

Smith had yet to be transferred to federal custody and was still being detained at the Cedar County Jail in Tipton on Monday afternoon. Sheriff Warren Wethington told the Associated Press that Smith was being held in her own cell.

"I don't feel comfortable putting her in with the general population due to the circumstances and media coverage other inmates would have seen," Wethington said. "Some of the inmates over there are mothers, sisters, nieces and aunts. I don't think it would be in the interest for her safety."

Smith was arrested early Thursday morning in West Branch, Iowa, on an unrelated Texas warrant after she spoke via cellphone with an officer who had instructed her to pull over at the nearest gas station.

According to an FBI affidavit, police found Smith had a prosthetic belly, baby clothing, a car seat and a stroller in her car, but not the baby. A search of her emails and Facebook account showed she had been claiming she was pregnant, but a pregnancy test was administered at the jail and it came back negative.

Police canvassing West Branch found the baby alive and well mid-morning Friday at another gas station along the interstate, more than 28 hours after a West Branch officer detained Smith.

Smith, who had initially denied abducting her nephew, admitted to authorities Friday she took the child and left him at the gas station, according to the FBI affidavit. She also made a hand-drawn map of the location where the baby was found in a plastic crate and wrapped in blankets.

An emergency room doctor at University of Iowa Hospitals and Clinics said it would be a miracle if the infant did in fact survive more than 28 hours in subzero temperatures, even inside the container.

"A child that young just doesn't keep himself regulated very well, so lasting that long is pretty impressive, if that's the case," said Dr. Joshua D. Stilley.

Holihan, the West Branch chief, told the Press-Citizen the plastic bin was covered in frost before he opened it, and he believed it had been there for "an extended period of time."

"With a newborn, the expected time in below-zero weather with no clothing at all would probably would be on the order of minutes before they got hypothermia, and less than an hour before it becomes terminal," Stilley said. "I know the baby was found in a container wrapped in blankets, so I'm sure that helps insulate the baby pretty well."

The child was found shortly after 10 a.m. Friday, and by early evening, UIHC said the child had been discharged to family, in good condition and unharmed by the cold.

Stilley said the hospital has been seeing a higher number of hypothermia and frostbite cases during this particularly cold winter, and conditions overnight Thursday into Friday were as bitter as ever. Temperatures dropped as low as minus-11 degrees Friday morning and minus-23 degrees with wind chill.

"That would be a miracle for a child to last that long," Stilley said.

Smith has an extradition hearing scheduled Friday on the Texas charge, but authorities said they believe her next move will be to Wisconsin because the federal case gets top priority.

Federal prosecutors in Madison have issued an arrest warrant for Smith, which gives them the power to place her in federal custody anytime. They will likely wait at least until a grand jury hands down an indictment, which could happen next week.