"We have not confirmed he acted alone," prosecutor Michael Von Zamft said Wednesday at a hearing on whether to unseal the affidavit for suspect Tyler Weinman's arrest.
Weinman, 18, was arrested June 14 and charged with killing and mutilating the cats.
Wednesday, the Miami Herald and CBS asked Miami-Dade Circuit Judge John Thornton to unseal the affidavit, saying it's a public record.
But prosecutors said releasing the affidavit could jeopardize efforts to investigate other possible suspects, the Herald reported.
Thornton refused to release the document, but prosecutors agreed to do so at Weinman's July 6 arraignment because the investigation is expected to be complete by then, the Herald reported.
Authorities have begun a separate investigation into threats against Weinman, Von Zamft said at Wednesday's hearing.
In Lauderhill, Fla., authorities have determined 17 cats found dead likely were not killed by humans, the South Florida Sun-Sentinel reported. That conclusion is based on necropsies done on the cats, the newspaper said.