Sometimes the black letter law passed by the legislature is unclear. The legislature can’t anticipate every possible fact scenario when they pass a law, so it lay to the courts to interpret the law and give guidance to what it means. This interpretation is called case law. When the court decides a certain meeting to the law it essentially answers a legal question. Lawyers and other courts then can rely on that ruling when they have a similar issue in their case. The following case answers the question above.

Illinois v. Gates, 462 U.S. 213 (1983).

This case addresses the following issue:

When, if ever, can an anonymous tip constitute probable cause to issue a search warrant?

This case asked the Court to reexamine a line of cases dealing with when probable cause is established, known as the Aguilar-Spinelli test. Id. at 228. This test requires a two-step inquiry to determine if probable cause to issue a warrant exists based upon information from an informant. Id. at 228-29. First, a “basis of knowledge” must be established, and then the “veracity” and reliability of the informant is judged. Id. at 229. Naturally, under this test an anonymous informant would always fail the veracity prong, because there could be no determination of the credibility of an unknown person. Id. The Court instead adopted a test which looks to the totality of the circumstances to determine if probable cause exists. Id. at 231.

In this case, an anonymous letter was mailed to police in Illinois. Id. at 225-26. It detailed a drug operation in which the criminal defendants were involved, whereby a car was driven to Florida empty and driven back filled with drugs to sell. Id. A detective decided to follow up on the letter, locating the defendants. Id. at 226. The detective then verified that the travel arrangements laid out in the letter occurred just as predicted. Id. Based upon these observations and the letter, the detective was issued a search warrant which produced evidence of the sale of drugs. Id. Applying the two-prong test, the Illinois Supreme Court determined that probable cause did not exist to support the issuance of the warrant because the anonymous informant’s veracity could not be determined. Id. at 229-30.

The Court disagreed with the application of the two-prong approach in these circumstances, though it acknowledged that “an informant’s ‘veracity,’ ‘reliability,’ and ‘basis of knowledge’ are all highly relevant” to a probable cause determination. Id. at 230. However, these are simply some of the factors that should be considered by courts in determining if probable cause exists. Id. The Court noted this “totality-of-the-circumstances approach” is the better test for probable cause. Id. at 231. This is particularly true when dealing with tips of “many shapes and sizes from many different types of persons.” Id. at 232.

The Court was very hesitant to affirm the Aguilar-Spinelli test, which it viewed as a “complex superstructure of evidentiary and analytical rules.” Id. at 235. Instead, the Court found the totality-of-the-circumstances approach to be better suited for the “nontechnical, common-sense judgments of laymen” and hurried situation in which warrants must be issued. Id. at 236.

Under the new approach, when an anonymous tip—such as the one here—can be coupled with verified information and other facts, probable cause exists. Id. 237-38. The Court noted the similarities between the present case and Draper v. United States, 358 U.S. 307 (1959). Id. at 242. Draper also dealt with an informant’s information being verified by a law enforcement officer. Id at 242-43. There, just as in the present case, the Court found that the real-time verification of what the informant predicted was sufficient to constitute probable cause—the fact that informant was anonymous in this matter did not defeat such a finding under the new approach. Id. at 243.