'She Just Didn't Want to Disappoint Him'

July 7, 2010— -- 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.

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.