An affidavit obtained by ABC News from the Montgomery County police states that McClain admitted to shooting Golden and taking the baby.
According to the affidavit, McClain's sister, Corina Jackson, had recently said that her sister would be adopting a baby soon. After she allegedly killed Golden and stole her newborn, McClain stated to her sister that she now had the child. McClain has three children ages 16, 10 and 6.
"There were statements that were made by Ms. McClain that led us to believe this was an intentional act on her part, not that Ms. Golden was targeted specifically, but that this was part of a plan to kidnap a child," Ligon said.
McClain, a mother of three, made her first appearance in magistrate court this morning. According to the Montgomery County district attorney's office, she was charged with capital murder early this morning.
"She's given a full statement to the detectives with the Montgomery County Sheriff's Department," the district attorney, Brett Ligon, said today on "Good Morning America." "As part of the statement with that agency, in conjunction with the other evidence that we were able to obtain yesterday...we did charge her [McClain] in the early hours of this morning with capital murder."
Though witnesses from the scene of the crime had told authorities there were two people in the car, police today said they are convinced that McClain had acted alone.
KEVIN DOLAK, KATIE KINDELAN, and DEAN SCHABNER contributed to this report.