In Coolidge v. New Hampshire (1971) 403 U.S. 443, the plurality opinion of Justice Stewart states: "It is well established that under certain circumstances the police may seize evidence in plain view without a warrant. But it is important to keep in mind that, in the vast majority of cases, any evidence seized by the police will be in plain view, at least at the moment of seizure. ( Id., at p. 465.)
"What the 'plain view' cases have in common is that the police officer in each of them had a prior justification for an intrusion in the course of which he came inadvertently across a piece of evidence incriminating the accused. The doctrine serves to supplement the prior justification -- whether it be a warrant for another object, hot pursuit, search incident to lawful arrest, or some other legitimate reason for being present unconnected with a search directed against the accused -- and permits the warrantless seizure." ( Id., at p. 466.)
Coolidge v. New Hampshire sets forth three requirements for the applicability of the plain view doctrine: (1) there must be a prior lawful intrusion of the area where the view takes place; (2) the discovery of the seized items must be inadvertent; and (3) it must be immediately apparent to the police that they have evidence before them.
The United States Supreme Court ruled that a magistrate's involvement with the investigative or prosecutorial arm of law enforcement may preclude him from comporting with the spirit of the Fourth Amendment's requirement that search warrants shall issue only after probable cause has been found by a "neutral and detached magistrate." In Coolidge the magistrate who issued the warrant was the state attorney general acting as a justice of the peace. The attorney general had been in charge of the investigation and was later to be chief prosecutor at trial. ( Id., at pp. 446-447.) The Supreme Court invalidated the warrant because "prosecutors and policemen simply cannot be asked to maintain the requisite neutrality with regard to their own investigations -- the 'competitive enterprise' that must rightly engage their single minded attention." ( Id., at p. 450.)
Coolidge rejected the state's argument that the search could be upheld on the basis that the issuing magistrate did in fact act in a neutral and detached manner. The court invoked a per se rule of disqualification. It also rejected the argument that the magistrate's lack of neutrality was irrelevant because the showing of probable cause was so strong that any magistrate would have issued a warrant based upon that showing. ( Id., at pp. 450-451.)
Thus, Coolidge stands for the proposition that in determining whether the magistrate is "neutral and detached" for Fourth Amendment purposes, primary importance is placed on the objective external circumstances and how they could be expected to influence a magistrate's decision whether to issue a warrant and not on the subjective state of mind of the particular magistrate. The United States Supreme Court held that "plain view alone is never enough to justify the warrantless seizure of evidence. This is simply a corollary of the familiar principle . . . that no amount of probable cause can justify a warrantless search or seizure absent 'exigent circumstances.' Incontrovertible testimony of the senses that an incriminating object is on premises belonging to a criminal suspect may establish the fullest possible measure of probable cause. But even where the object is contraband, this Court has repeatedly stated and enforced the basic rule that the police may not enter and make a warrantless seizure."