The victim has been identified as Patricia Belizaire, 25, of North Brunswick, N.J. Belizaire was the child's mother.
The little girl was abandoned in Newark, Delaware over the weekend.
Jackson was charged in Middlesex County on Thursday with a count of first degree reckless endangering for leaving the child in a bathroom at the gas station last Sunday.
Richard Sedlak from western Pennsylvania is a power company lineman who was passing through on the way to a job in Maryland. He stopped, intending to use the bathroom at a Shell gas station at 804 South College Avenue, near the University of Delaware. He got a key from the attendant and headed to the door, but heard crying from inside.
"He waited a few minutes, thinking there was a parent and child inside," said Lt. Brian Henry of the Newark Police. "But when the crying continued and nothing else happened he opened the door and found the child inside, alone."
After the child's picture was aired on television, including Eyewitness News, police received tips and were able to identify the girl.
The gas station where she was abandoned has an electronic surveillance system, but it wasn't working, investigators said.
The girl, who was living with her mother in North Brunswick, N.J., currently is in good health. She is in the custody of the Division of Family Services in Delaware.
After the child was found, an investigation by the Middlesex County Prosecutor's Office and the North Brunswick Police Department preliminarily determined that Jackson killed Belizaire in North Brunswick and drove the victim to New York, where the body was set on fire in a park shortly before 5:22 a.m. on February 22, 2010.
The cause of death is believed to be asphyxiation. Authorities said she was dead before her body was set on fire.
Now that Jackson is charged with murder, his bail has been increased to $2 million. He remained at the Middlesex County Adult Correction Center in North Brunswick, N.J.