In misdemeanor cases in New York City (and surely many other American venues today), the prosecution typically offers an “ACD”—an “adjournment in contemplation of dismissal.” That means that if the defendant doesn’t get arrested again in six months, the arrest is expunged. Often, the ACD entails the defendant spending anywhere from one to three days in community service, cleaning city parks. Sometimes, paying restitution is also involved on paper.
However, there is no guarantee that the authorities will follow up on the perp, to ensure that the punishment is carried out, and/or restitution paid. But it helps keep the official crime rate down.
Thus, there are people like Deanne Ostbye who constantly commit crimes that are virtually all “disappeared.” The same person might commit thousands in a lifetime, in which the police refuse to arrest the perp, talk the victim out of pressing charges, or the perp is arrested and gets an ACD.
Another type of case is where a black (typically a female) commits a racially motivated assault against a white, and a bystander (typically a black woman, but even liberal white women have been known to play this game) lies to police, and says that the white vic was actually the perp, and the black perp was actually the vic. White witnesses never intervene to set things aright in these situations, though they sometimes show sympathy to the vic and leave, before the arrests are made. Either the white vic gets arrested, and goes the ACD route, or (if the black perp has inflicted wounds on the white vic) they are both arrested. If both are arrested, the city lawyers get both parties to drop their respective charges in court, and the crime is thereby disappeared. Police always treat the black female perp with the greatest deference, even when they see the bloody wounds she has inflicted on her victim, while she has no marks on her.
Personal note: In January, 1991, a beefy Puerto Rican dyke sucker-punched me on a packed subway train during rush hour. She already had an arrest history for the same thing, but got an ACD, which included paying me $100 or $120 compensation for my broken eyeglasses. She never paid a dime. When I called NYC Victims’ Services to complain, I got a young-sounding white guy who told me that he’d had the same experience: He was assaulted, the perp got an ACD based largely on a promise to pay restitution, never paid a dime, and never was punished.