The (Belleville) News-Democrat reports that 30-year-old Ebony Jackson left her Oklahoma home Wednesday morning to visit relatives in St. Louis and East St. Louis, Ill., but never returned.
Her 3-month-old son, Donovan Prom, was found in a St. Louis County apartment building on Friday.
Police say the infant was left in the apartment's hallway, strapped in his car seat with a full bottle of milk. He wasn't injured.
Family members fear foul play was involved in Jackson's disappearance, but they also don't know if she had medical issues.
Jackson was last seen in Oklahoma by her boyfriend, who's also the baby's father.