when made in the course of police interrogation under circumstances objectively indicating that the primary purpose of the interrogation is to enable police assistance to meet an ongoing emergency. They are testimonial when the circumstances indicate that there is no ongoing emergency, and that the primary purpose of the interrogation is to establish or prove past events potentially relevant to later criminal prosecution. The Davis Court noted several factors that, objectively considered, help determine whether a statement is testimonial: Whether the statement describes past events or events as they are happening; Whether the purpose of the statement is to assist in investigation of a crime or, on the other hand, provide information relevant to some other purpose; and The level of formality of the exchange in which the statement is made. The court noted that a single conversation with, for example, a 911 operator may contain both statements that are intended to address an ongoing emergency and statements that are for the purpose of assisting police investigation of a crime. The latter are testimonial statements because they are the sort of statements that an objectively reasonable person, listening to the statements, would expect to be used in an investigation or prosecution. Availability If a statement is testimonial, the person making the statement must generally be available for cross examination. An exception to this rule is if the witness is unavailable. But even where the witness is unavailable, the defendant must have had a prior opportunity to confront the witness through cross examination. A witness may be unavailable for a variety of reasons. A common reason for a witness to be unavailable is that the witness is claiming a Fifth Amendment privilege against self incrimination. Other privileges are also a source of unavailability. Witnesses may also be unavailable because they have died, had memory loss, or simply decided not to cooperate as a witness against the defendant. The obvious may also occur, a witness may be intimidated, seriously injured, or murdered, and his prior statements then are usually not admissible even if it appears the defendant caused the nonappearance. The federal witness protection program was developed because of the difficulty of prosecuting cases where witnesses would disappear shortly before trial. These programs frequently require the witness to leave his residence or even family so that he can be protected before the trial occurs. Cross-examination Even where the witness is unavailable, the