Investigators said that Fucci had also told several friends that he planned to kill someone, though it wasn't clear whether Bailey was his intended target from the beginning, Larizza said.
Bailey was last seen early May 9 at the community centre in the Durbin Crossing community south of Jacksonville. Bailey and Fucci attended nearby Patriot Oaks Academy, where Bailey was a cheerleader.
Bailey's parents reported her missing later that morning, and a neighbour found her body in a heavily wooded area that evening, the St Johns County Sheriff Office said.
Fucci was arrested the next day on a second-degree murder charge.
According to an arrest report, video surveillance from the community centre showed the girl walking with Fucci shortly after 1am May 9. Another video from a nearby home showed the pair walking along a road about 1.45am.
The same video showed only Fucci walking in the areas at 3.27am, the report said.
The videos led the detectives to talk to Fucci.
The girl's body was found close to the boy's home, the report said.
Detectives reported finding evidence related to the clothing seen in the surveillance videos in the boy's bedroom. And some of the items had a presumptive positive result for the presence of blood, the report said.
A dive team found a knife in a nearby pond that investigators believe was the murder weapon.
