Due to a recent media frenzy involving a popular singer charged with assault, I was asked to give an opinion as to the likelihood that the State can prosecute a defendant when the star witness decides not to testify.  The State is not completely dependent on the star witness in every case.
As long as the State can prove the elements of the crime with evidence that will be introduced at trial, the State is not required to call any witness.  The admissibility of the evidence is crucial though, because if the evidence does not come in, the jury will never see it.  So then, it becomes a case-by-case basis to decide whether the evidence is sufficient to prevail.  Things such as 911 tapes, statements made to others (especially medical personnel), medical records, bloody clothing and other items, cell phone records, and photographs can all be used to help the State make its case against an alleged criminal. Unfortunately, because the State’s burden of proof is so high, there are cases where the circumstantial evidence is not enough to convict the defendant and a witness’ refusal to testify results in a criminal going free.