The Sixth Amendment of the federal Constitution provides that a defendant has the right to confront the witnesses against him. In Crawford v. Washington (2004) 541 U.S. 36, the United States Supreme Court held that admission of a "testimonial" hearsay statement by a declarant who does not appear for cross-examination at trial violates the confrontation clause unless the witness is unavailable to testify at trial and the defendant had a prior opportunity to cross-examine the witness. (Crawford, supra, 541 U.S. at pp. 59, 68.) This rule applies even if the statement is otherwise admissible under a hearsay exception. (Id. at pp. 50-51, 56 & fn. 7.) However, the confrontation clause does not bar admission of hearsay statements that are not testimonial. (Davis v. Washington (2006) 547 U.S. 813 (Davis).) Relevant to the parameters of testimonial statements to which the confrontation clause applies, Crawford explained: "The Confrontation Clause ... applies to 'witnesses' against the accused--in other words, those who 'bear testimony.' ... 'Testimony,' in turn, is typically 'a solemn declaration or affirmation made for the purpose of establishing or proving some fact.' An accuser who makes a formal statement to government officers bears testimony in a sense that a person who makes a casual remark to an acquaintance does not." (Crawford, supra, 541 U.S. at p. 51.) However, not all statements to government officers are testimonial. In Davis, the court formulated the following test to distinguish nontestimonial from testimonial statements made to law enforcement officials: "Statements are nontestimonial 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 objectively indicate that there is no such ongoing emergency, and that the primary purpose of the interrogation is to establish or prove past events potentially relevant to later criminal prosecution." (Davis, supra, 547 U.S. at p. 822.) The Davis court reasoned that statements to government officials that are "solely directed at establishing the facts of a past crime, in order to identify (or provide evidence to convict) the perpetrator" satisfy the definition of a testimonial statement because they are a solemn declaration or affirmation made for the purpose of establishing or proving some fact. (Davis, supra, 547 U.S. at p. 826.) Further, a witness's description of past events to an investigating officer may be testimonial regardless of whether the statements were reduced to a writing signed by the declarant or merely embedded in the memory or notes of the officer. (Ibid.) Davis acknowledged that "formality is indeed essential to testimonial utterance," but stated the requisite formality and solemnity exist when a witness describes past events to an officer, because deliberate falsehoods to officers constitute a criminal offense. (Id. at pp. 826-827, 830, fn. 5.) Davis also observed that even when statements were made without any detailed interrogation (i.e., volunteered statements or answers to open-ended questions), this does not automatically make them nontestimonial. (Id. at p. 822, fn. 1.) Under these principles, statements made to a 911 operator describing events as they are actually happening are not testimonial if their purpose was to provide the police with information necessary to resolve a present emergency and they were made in an environment that was not tranquil or safe. (Davis, supra, 547 U.S. at pp. 827, 828.)