The child was found Friday in seemingly good health in an eastern Kansas home. A red hatchback similar to a description offered earlier by police was in the driveway.
Lisa M. Montgomery, 36, of Melvern, Kansas, was arrested later Friday and charged with kidnapping resulting in death.
Authorities say Bobbie Jo Stinnett, 23, was found Thursday in a pool of blood inside her small white home in Skidmore, a town in northwest Missouri.
Earlier, Stinnett, who was eight months pregnant, had been talking with her mother on the phone, and hung up saying a woman she had chatted with online had just arrived at her door, authorities said.
Stinnett's mother found the 23-year-old nearly dead. Paramedics tried to revive her, but she was pronounced dead at a hospital.
U.S. Attorney Todd Graves said Montgomery contacted Stinnett through an online message board, and authorities zeroed in on her using computer forensics. Montgomery told Stinnett she was seeking to buy a dog from Stinnett, who raised rat terriers, he said.
Graves noted that Montgomery's screen name on the Internet message bulletin board where she contacted Stinnett was "fisherforkids."
The Washington Post says in its Saturday editions that it was "fast sleuthing by the FBI and private computer security specialists who traced e-mail messages to Montgomery's house…(that) led investigators to the baby."
Stinnett, married for a little more than a year and expecting her first child, worked at an engine factory in nearby Maryville. Her husband was at work when she was killed, authorities said.
The baby was named Victoria Jo and was united with her father, Zeb Stinnett, late Friday, Stormont-Vail Regional Health Center in Topeka said in a statement Saturday on its Web site. She was listed in good condition at the hospital's neonatal intensive care unit. Zeb Stinnett called the girl "a miracle."
"I want to thank family, friends, Amber Alert and law enforcement officials for their support during this time," Stinnett said in the news release.
CBS News.com found messages of concern on the mesage board of the Web site of the Stinnett dog breeding service, whose sadly ironic name is Happy Haven Farms.
Among them: "Zeb: I read about the horrible thing that happened to you and your family and had to send you my deepest sympathy. You are in my familys prayers. Also: "Zeb: I have you in my prayers. I am so sorry for your loss. ...I hope justice is served."
Montgomery is the mother of two high school-aged children, but Graves said she had been pregnant with another child that was never born.
It's unclear when she lost the baby or under what circumstances, but the complaint said she had lied to her husband about giving birth. Graves declined to give a motive for the crime.
According to the criminal complaint, Montgomery traveled about 40 miles to Topeka, Kansas, on Thursday to go shopping. Her husband received a call from her saying she had gone into labor and given birth.
Kevin Montgomery and the couple's two children met Lisa and the newborn at a parking lot in Topeka and drove home, according to the affidavit.
The next day, authorities say, Montgomery confessed that she strangled Stinnett from behind, laterally cut her open, removed the baby and cut her umbilical cord. She also admitted that she lied to her husband about the ordeal.
Although DNA tests were pending to confirm the baby's identity, authorities called off the Amber Alert issued for the child.
"We're confident we have the little girl that was taken from Skidmore," Nodaway County Sheriff Ben Espey said.
Espey said he believes Stinnett resisted the attack.
The grisly slaying shocked neighbors in the towns where the two women lived.
"They're very normal country people," said Sandra Bullock, 45, who lives about a mile down the road from the Montgomerys. "It's too hard to believe."
Stinnett's neighbor Bill Dragoo was equally surprised.
"It blows my mind that this happened," he said. "She was such a shy person. They didn't deserve this."
Missouri State Highway Patrol Sgt. Sheldon Lyon said the investigation was ongoing. He would not say if additional charges might be filed or if there were other suspects.
Several pregnant women have been killed in recent years by attackers who then removed their fetuses, in some cases to pass the children off as their own.
In one of the most recent cases, a 21-year-old woman was shot to death in Oklahoma in December 2003, allegedly by another woman who pretended the 6-month-old fetus was her child. The fetus died. The woman accused in the case was found incompetent to stand trial and is undergoing treatment in a mental hospital.