TOWN OF BELOIT, Wis. >> An hour after a woman reported her newborn son missing from a Wisconsin home, police were questioning her step-sister — found with a prosthetic pregnancy belly, baby clothes and a stroller, but no baby, according to court documents.

It was more than 24 hours after Kayden Powell went missing before authorities discovered the infant, less than a week old, in a plastic storage crate outside an Iowa gas station, miraculously alive and well despite frigid temperatures.

Kristen Smith of Denver had pretended to be pregnant, went to Wisconsin and stole her step-sister’s baby from his bassinet as his parents slept, court documents say. Then, as police closed in on her, she allegedly abandoned the infant, who was swaddled in blankets.

Federal prosecutors in Madison charged Smith with kidnapping Friday afternoon, hours after an Iowa police chief found Kayden.

“He’s strong,” the newborn’s great-uncle, Mark Bennett, said of the boy. “I’m glad that baby is still living instead of in a ditch somewhere on a strange highway.”

The discovery of the infant shortly after 10 a.m. Friday capped a frantic search that involved police officers in Wisconsin, Illinois and Iowa.

It began after the boy’s mother, Brianna Marshall, called police around 4:30 a.m. Thursday to report her newborn had vanished from Bennett’s home, where she and the baby’s father, Bruce Powell, had been staying, according to police and the affidavit.

Marshall said Smith had left the house a couple of hours earlier to return to Colorado. While police were at the house, Smith called on her cellphone. She told police that Marshall and Bruce Powell were planning to move to Denver on Saturday to live with her and she had Kayden’s clothes in her car but didn’t have the boy.

Police told her to pull over for questioning. An officer met her at a Kum & Go gas station near Interstate 80 in West Branch, Iowa. She was arrested about 5:30 a.m. on an outstanding Texas warrant, but she denied any knowledge of Kayden’s whereabouts, the affidavit says.

A search of her cellphone revealed emails in which she said she gave birth on Feb. 5, according to the court document. A search of her Facebook page turned up postings in which she claimed she was pregnant.

Smith didn’t appear pregnant, according to the affidavit. A pregnancy test that was administered while she was in custody came back negative, U.S. Attorney John Vaudreuil said.

Meanwhile, dozens of officers began searched for the child at possible stop-offs along Smith’s route from Wisconsin to Iowa. West Branch Police Chief Mike Horihan decided to check the area around a BP station about 500 yards from the station where Smith was arrested. He heard a baby’s cries and discovered Kayden in a closed storage crate alongside the building. The newborn was responsive and healthy, the chief said.

“I had tears in my eyes,” BP station manager Jay Patel said, recalling his reaction to the police chief telling him that the infant had been found. “It’s good news, but it’s sad, too.”

Temperatures in West Branch, about 180 miles southwest of the Town of Beloit, dipped below zero Thursday night into Friday. They were still in the single digits when the baby was found.

“Surprisingly with the weather the way it was, he was surprisingly healthy,” Horihan, the Iowa police chief, said. “To be honest with you, that’s not what I expected.”

The baby was taken to an Iowa City hospital, where he was reunited with his parents and released Friday evening.

Online court records didn’t list a defense attorney for Smith. She faces life in prison if convicted.

Police interviewed Smith again after Kayden was discovered, the affidavit said, and she admitted she had taken the baby and left him at the BP station.

Bennett, the baby’s great-uncle, told The Associated Press he first met Smith on Thursday night, when he came home and found her, his mother and the baby’s mother and father in his house. He said his mother later explained to him that Marshall and her step-sister had the same father but different mothers.

He went to his room in the basement. When he woke up, the baby and Smith were gone.

He said he kept telling Marshall that Smith had to have taken the child, but Marshall refused to believe it. The baby’s bassinet was 2 feet from the parents’ bed and he found a paring knife on the ground next to it.

“I could have woke up to a bloody mess,” Bennett said.

He said he hopes Smith gets locked up for life.

“You stole him like you’re stealing something from the grocery store,” the great-uncle said. “Nobody in their right mind should have thought of that.”

Smith appears to go by multiple names and has had run-ins with the law in multiple states, authorities said. The Texas warrant stems from a felony indictment charging her with tampering with government documents late last year while she was in jail in Colorado.

A spokesman for the Arapahoe County, Colo., sheriff’s office declined to discuss the details of her arrest there. A spokeswoman for the district attorney’s office in Tarrant County, Texas, said it’s not clear why Colorado authorities released Smith instead of sending her back to Texas.

Foley reported from West Branch, Iowa. Associated Press researcher Rhonda Shafner in New York and writer Taylor W. Anderson in Madison, Wis., contributed to this report.