Sixth Amendment Confrontation Clause
The Sixth Amendment states:
“In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the state and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the assistance of counsel for his defense.” 
The Sixth Amendment Confrontation Clause provides the defendant in a criminal proceeding with the right to confront witnesses against him in court. It gives the defendant the opportunity to cross examine the witness to either impeach or clarify the testimony. The question of whether statements made to police during the investigation of a crime, which were not made with the intent to preserve evidence, should be admitted in is answered in Crawford v. Washington.  In this case, the court held that the statements should not be admitted in court without allowing defendants to cross-examine the person who made the original statements.
For the purposes of the Confrontation Clause, to distinguish admissible statements from non-admissible statements, the Court poses a two-prong test to determine the availability of the witness. A good example of the test in action is exhibited in Johnson.  Mr. Johnson was confronted with drug charges. The State of Florida performed laboratory testing to provide evidence against Johnson.
However, the technician who performed the test had left the state to work elsewhere. Johnson claimed the drug test results was testimonial hearsay and because he could not confront the technician who conducted the testing that the evidence should not be admissible. Because the State of Florida did not want to incur the cost of making the technician available to testify, the State labeled the test results as a business record. Business records are admissible. 
The Court held that Florida had the opportunity to secure the witness for testimony, but failed to do so.
It then held that because of the nature of the lab testing (to provide evidence against Mr. Johnson), the evidence was not merely a business record, but was indeed testimony subject to the confrontation clause.
The reason the Court makes a distinction about what is admissible or what is testimonial is that for instance, in Johnson, the State attempted to introduce damaging evidence against Johnson without allowing Johnson the ability to attempt to either clarity (to his advantage), or impeach the evidence by a confrontation with the witness.
If the statement or evidence is being used to help prosecute the defendant, then the Confrontation Clause must be invoked to protect the defendants Sixth Amendment rights. However, in Davis, when the victim made statements both in response to questions asked by police as well as other points of information, the Court rationalized that she did so in the context of reporting a crime and identifying a suspect.  Because of that fact, the Court did not consider the statements to be testimonial and not subject to the Confrontation Clause.
 U.S. Const. amend. VI.
 Crawford v. Washington, 541 U.S. 36 (2004).
 State v. Johnson, 982 So. 2d 672 (Fla. 2008).
 Davis v. Washington, 547 U.S. 813, 126 S. Ct. 2266, 165 L. Ed. 2d 224 (2006).