Aguilar-Spinelli test

The Aguilar–Spinelli test was a judicial guideline set down by the U.S. Supreme Court for evaluating the validity of a search warrant or a warrantless arrest based on information provided by a confidential informant or an anonymous tip. The Supreme Court abandoned the Aguilar–Spinelli test in Illinois v. Gates, 462 U.S. 213 (1983), in favor of a rule that evaluates the reliability of the information under the "totality of the circumstances." However, Alaska, Massachusetts, New York, Tennessee, Vermont, and Washington have retained the Aguilar–Spinelli test, based on their own state constitutions.

The two aspects of the test are that, when law enforcement seeks a search warrant and a magistrate signs a warrant:

This information provided to a magistrate will allow the magistrate to make an independent evaluation of the probable cause that a crime has been or will be committed.

When a warrantless arrest occurs based on information provided by a confidential informant or anonymous source, for the arrest to be lawful, the police must establish that the information relied on in making the arrest meets the same two basic elements described above.

At a post arraignment hearing the police must:

(1) demonstrate facts that show their informant is reliable and credible, and

(2) establish some of the underlying circumstances relied upon by the person providing the information.

If prior to trial, the police cannot establish both prongs of the test, a judge may dismiss the case for lack of probable cause to make the warrantless arrest.

According to the Fourth Amendment to the U.S. Constitution:

Historically in the United States, if the police made an illegal search and seizure of evidence, the evidence, once obtained, could often be used against a defendant in a criminal trial regardless of its illegality.

By a unanimous decision in the case of Weeks v. United States, 232 U.S. 383 (1914), the Supreme Court adopted the "exclusionary rule". This rule declared that, in most circumstances, evidence obtained through an illegal search and seizure could not be used as admissible evidence in a criminal trial. (This decision adopted the rule only on the federal level. It was not until Mapp v. Ohio, 367 U.S. 643 (1961), that the exclusionary rule was held to be binding on the states through the doctrine of selective incorporation.)

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