Police have found the body of a woman whose infant was abandoned at a St. Louis County apartment complex, and are now searching for whoever killed her.

The body of an Oklahoma City woman reported missing after her infant son was discovered apparently abandoned in the hallway of a St. Louis County apartment complex has been found in the trunk of her car in a desolate street of St. Louis, police said.

Authorities had been searching for 30-year-old Ebony Jackson since her 3-month-old son was found unharmed at 5 a.m. Friday in the complex in Breckenridge Hills.

Police obtained a court order Tuesday morning to activate a GPS tracker for Jackson's 2004 Mitsubishi Galant, which led them to a St. Louis street lined mostly with vacant lots and crumbling homes, The St. Louis Post-Dispatch (http://bit.ly/VE3AvR ) reported. At least one neighbor told police that the car, with Colorado plates, had been there for days.

Breckenridge Hills police obtained a search warrant to open the trunk around 5 p.m. Tuesday. Jackson's decomposed body was inside.

The St. Louis County medical examiner will conduct an autopsy. St. Louis police are leading the homicide investigation.

Jackson is originally from East St. Louis, Ill., but she had moved to Oklahoma City and recently returned to the St. Louis area for a visit but relatives. She had not been heard from her since Thursday.

Relatives said doctors discovered Jackson had a brain tumor when she was a teenager. Surgeries did not remove it entirely, and a shunt drained fluid and pressure from her brain.

Jackson's cousin, Tondra Mosley of Los Angeles, said the woman worked as a sales representative at a Macy's store and lived with her child's father, Craig Prom, in Oklahoma City.

Relatives became worried when they couldn't reach Jackson by cellphone on Friday after the baby, Donavon Prom, was found in a car seat in the heated apartment hallway. Jackson had no known connection to the apartment building.

Relatives said Jackson left her Oklahoma City home on Jan. 2. Craig Prom found a note saying she needed more space.

She went to her aunt's home in East St. Louis on Thursday, but no one was home. She and the baby visited a neighbor and she left about 10 p.m. Thursday, telling the neighbor she needed to find a place to stay for the night.

Jackson then called Mosley's mother saying she would stop by on Friday with the baby. That was the last relatives heard from her.

Linda Lawson, a family spokeswoman, issued a statement describing the family's "unimaginable heartache."

"Someone out there knows what soulless people did this: Please come forward to let us know before it's your loved one," the statement said.