Stephen Cortez Harper was indicted by a grand jury Thursday in connection with the first-degree murder of 8-year-old Paris Whitehead-Hamilton.
He is one of three suspects arrested in connection with the murder — but his case is the only one prosecutors have put before a grand jury so far.
Authorities say they're still building their cases against the others despite some hurdles.
Pinellas-Pasco Chief Assistant State Attorney Bruce Bartlett pointed to the "code of silence" that keeps witnesses from cooperating.
"There is no question that the reluctance of people to come forward … is hampering the police officers," he said.
Paris died April 5 after a gang shot up her home while aiming for a rival gang member staying inside, police said.
Harper, 18, was arrested on a charge of first-degree murder hours afterward. Police say he admitted to loading the rifles that were used and to being at the scene.
Police say it took at least two people to fire the more than 50 rifle bullets that pierced Paris' home, three of which hit the girl.
The only one accused so far of pulling a trigger is Dondre Davis, 19, who was captured along with Mario Lewis Walls, 18, after a four-day manhunt. Davis was arrested on a first-degree murder charge, while Walls was arrested on a charge of being an accessory after the fact.
St. Petersburg police Chief Chuck Harmon said the tips that helped end the manhunt have dried up. And some witnesses still have yet to come forward.
"Without the public's help, this is going to be a very difficult case for us to prosecute," Harmon said. "They're off the street, but we need the public's help in keeping them off the street."
A grand jury indictment is required to prosecute first-degree murder, which carries only two sentences upon conviction: life without parole or death.