'She Just Didn't Want to Disappoint Him'

After Stephanie Foster, 34, suffered her third miscarriage, the desire to have another child was so strong she would do anything to get one, police say.

Foster faked a pregnancy for nine months and then attempted to kidnap a child by attacking a young mother in her home, stabbing the woman in the back and arm, investigators say. The young mother, Ashley Speer, and her husband, Michael, were able to subdue Foster until police arrived.

VIDEO: An Indiana woman allegedly faked pregnancy and tried to steal a baby. Play
Woman Charged With Baby Snatching

Although Foster's alleged actions may seem strikingly bizarre, Dr. Michael Welner, a forensic psychiatrist, said Foster's behavior is in line with women who are desperate to save a troubled relationship.

Watch the whole story tonight on 'Nightline,' 11:35 p.m. ET "This isn't a crime about a loss of a baby; this isn't a crime about a miscarriage," he said. "In my professional opinion, this crime is about the loss of a relationship." Welner said the women involved feel they need to take action in order to save the relationship they believe is falling apart or one that has already been lost. "The baby is a means to an end," he said.

According to investigators, Foster searched spring birth announcements in the local Indiana paper, zeroing in on a baby boy born to Ashley and Michael Speer. In late June, police say Foster went to the Speers' home and asked to use their phone.

Vigo County Sherriff Jon Marvel is the lead investigator in the case. "Ashley let her in, used the telephone... she thanked her and out the door she went. The suspect returned again shortly just a few seconds later, again knocked on the door and asked if she could use the telephone again."

But what appeared to be an innocent call turned into attempted murder, said Sheriff Marvel.

"As they're walking down a short hallway going into the kitchen area, Mrs. Speer turned around… and saw the suspect pull out what appeared to be a gun," Marvel said. He described how Speer got hold of Foster's arm holding the weapon, a pistol BB gun. Foster then pulled a knife from her fanny pack and began stabbing the young mother in the arm, he said.

Marvel said Speer's husband and 1-month-old baby boy slept unaware in a different room. While Foster continued to stab Speer, and as they struggled, Speer was able to call 911.

According to Marvel, the 911 dispatcher could hear the commotion in the background, but said Speer "was relatively calm, telling the dispatcher what was going on, that there was a woman who she was struggling with, who was stabbing her with a knife, and could we get some help down there," Marvel said.

Eight minutes later, Indiana State Police Sgt. Joseph Watts arrived on the scene. Watts recalled looking through the door and seeing a young woman lying on the floor bleeding. "We forced open the door, went inside, and then located the husband and suspect in the living room," Watts said. Ashley Speer's husband, having awakened from the commotion and come to his wife's aid, had pinned their attacker to the floor.

"He was literally holding her down, awaiting our arrival," Watts said.

By then, Ashley Speer had suffered multiple stab wounds and was in critical condition.

Police: Suspect Stuffed a 'Pregnancy Pouch' to Fake Pregnancy

"She was stabbed many times in the back, many times in the arm.," Marvel said, and he described the scene. "There was blood from the rear kitchen door all the way thru the hallway, out into the kitchen and family room," he said. "It was a horrible, horrible scene."

He said he spoke with Speer briefly as paramedics rushed her to a waiting helicopter, but she looked in rough shape. "She gave all appearance of being a woman who was near death," Marvel said.

Speer was flown to an Indianapolis hospital 80 miles away, and her husband had suffered minor injuries in the attack, but he was not seriously hurt. Back at the county jail, Foster was starting to talk.

"She confessed to about everything," Marvel said. "Why she started that first lie, how it progressed, how she ended up down there, how she took out the knife and stabbed Ashley, [at first] in the arms, and then ultimately, in the back, trying to get away," he said.

He said Foster simply began confessing and told her whole story. The confession was startling -- even for Marvel, a detective with 36 years of experience. "I've never seen anybody that a detective didn't have to keep pulling it out," he said.

According to Marvel, Foster confessed she had convinced her husband she was pregnant by stuffing a pillow under her blouse. According to court documents, she continued to deceive those around her by purchasing baby clothes, while she prepared false birth certificates.

"She had committed a ruse here on her family, husband, mother, all of her friends, relatives, for nine months," Marvel said, recounting Foster's confession. Foster had three children from a previous marriage and was familiar with how she should look and act as her pregnancy progressed, according to police.

"She had sewn together what I call a pregnancy pouch, where she could add stuffing to it as the pregnancy went along," Marvel said.

Police said Foster confessed that she had carried on an elaborate deception for nine months, telling her family members she was going to doctor appointments and then returning with favorable progress reports on the non-existent fetus. Foster began lying to her husband, she reportedly told police, after suffering a third miscarriage with him. Foster said she didn't want to disappoint him, according to police.

Marvel said he believes Foster's motive in attacking Speer was to cover her tracks.

"I think she started out to cover a little white lie," he said. "Remember what your folks told you when you were growing up about telling one lie? You have to tell another and another."

"She had backed herself into that corner so tightly, that in her own mind she had no other avenue except to find a baby that she could produce that week," he said. With Foster having arrived at her "due date," Marvel said Foster told authorities that she knew she had to do something. "After nine months of deceit, [she] could not bring herself to tell everybody that, 'I was deceitful about this,'" he said.

According to Dr. Welner, this type of thinking is the mark of a woman desperate to save her relationship. Their extreme actions – in this case, attacking a woman to steal her child – demonstrate the lengths they are willing to go to claim a pregnancy.

Foster is not the first woman to make such an attempt. In 2004, Lisa Montgomery stalked a pregnant Missouri woman while faking a pregnancy of her own. Montgomery killed the mother and cut the baby from her womb. Montgomery is now on death row. In 2006, Shannon Torrez, had also suffered a miscarriage. She cut a young mother's throat and kidnapped her baby girl, passing it off as her own. The young mother survived, and Torrez is currently serving 30 years in prison. Last year, 21-year-old expectant mother Heather Snively's body was found dead in Korena Roberts' home. Police say Roberts met Snively on Craigslist and invited her over. She killed Snively and cut the baby from her womb, and she tried to pass the baby off as her own, police say. Roberts plead not guilty to the murder charges against her, and will go to trial this fall.

Welner said that although most people would consider these crimes outlandish, these women see it as a means to an end. "Ask yourself, how far would you go to steal a billion dollars? Would you kill someone for it? Would you stab them for it?" he said. "For the women behind this crime, being able to say 'I bore a child' is priceless. And these women would do anything for it."

Stephanie Foster faces charges of attempted murder, with a maximum penalty of 50 years in prison if convicted. Her defense attorney said says he plans to file an insanity plea.

Meanwhile, Ashley Speer is recovering from her injuries.

"She fought extremely hard," Marvel said. "She fought for her baby's life and then her own… This was purely animal instinct for this mother to protect her child that way. We see it on TV all the time with animals how they fiercely protect their cubs from any predators and this is exactly what this woman did to protect her child. She fought with her life," he said.

Speer's son slept soundly through the entire violent episode. He awakened only after police had arrived.