They're not saying stuff in public, though,
they're saying it to the prosecution. If they falsify their testimony to the state prosecution I'm fairly sure under American law that's a crime. Maybe there'll be a moment of courtroom drama where a witness dramatically changes his or her testimony, but at this point I'd take the stuff the witnesses are saying as "it". One of the witnesses also came forward before Zimmerman was charged and claimed that the
police misrepresented her testimony and refused to change it as well.