Jacinita and Mariano Soto - with their toddler and newborn baby in tow - had moved into a new neighborhood a few weeks ago, searching for a better and safer life.

Bothered by gang violence in their old neighborhood, they turned to a basement apartment on a quiet, tree-lined street on Chicago's North Side. If police are right, the events that led to their murder began when Jacinita Soto paid a simple visit to a doctor.It was there, authorities said, that Jacinita Soto and 2-month-old daughter Guadalupe Marie were spotted by 22-year-old Adriana Mejia, who plotted to kill the Sotos the very next day and snatch their children - all because she couldn't have a baby of her own.

"It's an unbelievable story," said Kevin Morison, a police spokesman.

Police said Mejia persuaded her 25-year-old cousin, Arturo Leon, and their 23-year-old housemate, Gabriel Solache, to help her carry out the plan in the early morning hours of March 28.

Police say Mejia paid Leon $600 to help with the plot, though it wasn't clear whether he was to split the money with Solache. All three were charged Sunday with first-degree murder, kidnapping and home invasion.

Mejia has tried unsuccessfully to have a baby since she got married four years ago, police said.

But she fooled her husband and friends into believing she was pregnant and, after deciding upon the Sotos' baby, told him she was going to the hospital to have her child, police said.

"She said, `I've had a baby girl. Pick me up in the morning,' " said police Commander Philip Cline.

That was late March 27 - the same night a suburban Chicago jury recommended a death sentence for Jacqueline Williams, convicted of killing two children in 1995 along with their pregnant mother, whose full-term baby was cut from her womb.

Investigators said Mejia did not mention that case. But they contend Mejia also turned to murder to get a child.

"She said they knew they were going to have to kill the parents to get the baby," Cline said, adding that all three suspects have admitted to a role in the killings.

According to police, Mejia led the others to the Sotos' apartment, where Jacinita Soto answered the door and was stabbed to death with one of two knives taken to the scene.

Her husband was killed as he slept, Cline said, and the suspects abducted the girl and her 3-year-old brother, Santiago. Police did not know whether the children witnessed the killings.

When Mejia's 23-year-old husband, Rosauro, picked her up later that day and asked about the little boy, she said she was caring for him because his mother had complications with her pregnancy, Cline said.

The bodies were found last Wednesday, and a far-reaching search began for the children.

On Friday, Rosauro Mejia saw the boy's picture on television and took him to a police station. Investigators found the girl with Adriana Mejia at her home - until then, police said, Rosauro Mejia did not realize the girl was being sought.