Motions filed in Volusia County, Florida district court on Thursday show that prosecutors are upgrading the charges and trying the 14-year-old boy as an adult with premeditated first-degree murder.
Fucci had initially been arrested on May 10 and charged with second-degree murder in Bailey's death. The teen will now be represented by the public defender's office.
Seventh Circuit State Attorney R.J. Larizza is expected to give an update on the investigation of the murder on Thursday afternoon.
"We appreciate the patience and support from family, friends, neighbors and all of the folks who have been following this disturbing case," a statement from the State Attorney's office said. "We are in the final stages of our comprehensive review of the facts, circumstances and the law. It is Mr. Larizza's intention to address several questions/issues that surfaced as a result of this brutal homicide at that time."
Bailey was first reported missing on May 9 and found dead later that day in a wooded area of St. Johns, Florida.
St. Johns County Sheriff Rob Hardwick told WJXT that the girl had been stabbed a "horrific" number of times, adding "the word accident is nowhere involved in this case."
The latest court motions come after a Change.org petition, which insists that Fucci is guilty for the crimes he has been charged with, gathered more than 700,000 signatures urging Larizza's office to charge Fucci, who was a classmate of Bailey's at Patriot Oaks Academy, as an adult.
"Tristyn Bailey was murdered. She was only 13. Her murderer is 14 and is being charged with second degree murder. But he should be tried as an adult," the petition reads.
The petition continued, "He showed no remorse for what he did. He posted on his Snapchat story a picture of him in a police car saying, '[Has anyone] seen Tristyn lately?' knowing he had just murdered her the night before. Tristyn deserves to have justice."
The sheriff's office said Fucci's story changed multiple times since the investigation began, but he ultimately made several admissions that were corroborated by surveillance video and other evidence.
"I can just tell you that the man is a cold-blooded killer, and I hate to say man because he's a child, but he committed a man's crime," Hardwick said. "With that being said, of course, I think he's being held responsible for the crime he committed."
Fucci has previously been in custody at the Department of Juvenile Justice facility in Daytona Beach since his arrest. He will be rearrested and moved to the jurisdiction of the adult court.