The abducted girl's after-school program at the day-care center was a block away from her Bryant Elementary School at 6001 Cedar Ave.
Prosecutors say they can't explain why Regusters allegedly abducted the child from her school and then sexually assaulted her so severely that she required surgery.
Walker told the jury of eight women and four men that Regusters' job application had two reference letters and that she passed FBI and state police background checks and one with a child-abuse database.
Yet Walker also said she suspended and then fired Regusters on Feb. 8, 2013, after a year on the job, when the 19-year-old teacher's assistant began chronically reporting late or calling out sick.
On Jan. 14, 2013, Regusters, now 21, allegedly donned Muslim garb that covered all but her eyes, went to Bryant at about 8:50 a.m. and took the girl out of her classroom, telling a substitute teacher she was the mother.
Authorities allege that Regusters took the child, hidden inside a laundry bag, to a house in the 6200 block of Walton where Regusters lived with an aunt and her family. There, Regusters allegedly terrorized the child, sexually assaulted her with an object, and then, early the next morning, left her at a park in nearby Upper Darby.
The girl helped police retrace her steps to the Walton Avenue house, leading to Regusters' arrest.
In other testimony Tuesday, Cindy Christian, a child-abuse pediatrician at Children's Hospital of Philadelphia who examined the child, called the injuries the child suffered among the most severe she had seen in thousands of child-abuse cases.
Regusters has maintained her innocence, and attorney W. Fred Harrison Jr. contends that others in the Walton Avenue house could have been responsible for the crime.
Walker, questioned by Assistant District Attorney Jessalyn Gillum, wept as she recalled the day the 5-year-old disappeared.
Walker said she had attended high school with the girl's mother and that her own daughter, 6, attended the center's after-school program and was friends with the kidnapped child.
"I really can't describe how I felt," Walker said. "I was scared, angry, upset."
The girl's disappearance was not discovered until about 3:30 p.m. that day when Carter, who picked up Bryant students daily for the after-school program, called in a panic to say that someone had picked up the child hours earlier.
Carter wept uncontrollably - and brought several jurors to tears - as she described the guilt she felt when she told the child's mother she was missing.
"It was my job to pick her up from school and she wasn't there!" sobbed Carter.
Regusters seemed unaffected by the emotion and sat taking copious notes during the testimony.
Walker testified that Regusters was acquainted with the victim and her siblings in the after-school program and would have been familiar with the interior and routine at Bryant Elementary.
When Carter was absent, Walker said, Regusters sometimes walked the children from Bryant to the day-care center.