Illinois v. Gates

Prior to Gates's trial, the respondents filed a motion to suppress the evidence, asserting the warrant that procured it had been obtained without "just cause." In legal terms, an anonymous tip is considered insufficient evidence for granting a search warrant. They were successful in this, and an appellate court upheld this decision suppressing all evidence. The Illinois Supreme Court also upheld the exclusion of evidence. All of these courts used two legal precedents in determining that the Bloomingdale police's search warrant was not valid. In the first, Aguilar v. Texas (1964), the courts had ruled that an informant's tip is enough to obtain a warrant if the police can determine the reliability of the source of this knowledge (for example, that the informant was a firsthand witness to it), and if the police can prove the informant's veracity in other areas. The Bloomingdale police's affidavit had neither.

Spinelli v. United States (1969), was another case used by courts to determine if a warrant was valid if it had not passed the requirements set forth in Aguilar v. Texas. Spinelli holds that there is "probable cause" to grant a warrant if some details provided by the tip are corroborated by police investigation, but if the informant presents evidence that may just be hearsay or rumor, this is not considered trustworthy. This was also a significant factor in barring evidence seized at the Gates home from incriminating them at their trial.