I could see them arresting solely on this persons story only if they got agreement from the person that they would testify to it in court. So if they dont have the tape itself I am assuming this person has agreed to testify to what they saw and heard. The interesting thing will be how the jury feels about what they say and what the defense questions to them will be. Questions like How do you know for sure the person you saw was Holly? How do you know for sure the person you heard was so and so? I just dont see that going too well unless there is corroboration from either another witness or the tape itself, which LE could have of course.