It happens perhaps most often in domestic violence cases that the complainant fails to show up on the morning of trial. The government would have you believe this is because the complainant fears for his/her safety, and this might sometimes be true. More often, it is because the complainant has reconsidered having the lover, spouse, or family member locked up now that things have settled down.
The government might prefer it this way anyway. Assuming the prosecutor can satisfy one of the hearsay exceptions and also convince the judge that any statements are not “testimonial,” the prosecutor can now base its case not on the unpredictable testimony of a civilian witness but on the steady and unchanging testimony of a trained police officer. The prosecutor knows what he or she will get — exactly what is written in the police report – and there is much less chance that the officer will waver or fall prey to the wily ways of defense counsel.
The problem is that, unless the defendant takes the stand him or herself, the court never hears from anyone who was actually present at the time the alleged offense occurred. Justice Sotomayor devoted over 11,000 words in Michigan v. Bryant to a “totality of the circumstances” discussion, objective versus subjective analyses, and other legal hairsplitting. The fact is, no matter how carefully you parse the issues, there is no substitute for the crucible of cross-examination in bringing the truth out at trial. Call my accuser before my face, said Sir Walter Raleigh. Let him speak his piece.