A search warrant affidavit based entirely on hearsay is not unconstitutional for that reason alone. The hearsay has to be credible and the collective knowledge doctrine is one way to do so. If probable cause is shown on the totality, it would be sufficient. State v. Morris, 2017 Del. Super. LEXIS 672 (Dec. 19, 2017):
An affidavit relying on hearsay “is not to be deemed insufficient on that score, so long as a substantial basis for crediting the hearsay is presented.” In warrant contexts, probable cause may be “founded on hearsay information provided to the affiant by other officers. … [A]n officer-informant relaying the information to the affiant will be considered a reliable source for the information needed to determine probable cause.” The United States Supreme Court has similarly held that hearsay observations of a warrant applicant’s qualified fellow officers are “plainly a reliable basis” on which a magistrate may rely in determining probable cause.
The United States Court of Appeals for the Eighth Circuit, in Gallagher v. United States, considered whether an affidavit composed entirely of hearsay is deficient, and reached its conclusion for reasons this Court finds persuasive:
At this point in the development of jurisprudence interpreting the Fourth Amendment, a claim that a search warrant is invalid because it is based entirely on hearsay is frivolous. … Particularly is this true in the now complex field of criminal investigation. … Unless authorities do act quickly upon an evaluation of reports received by them, the fruits of the crime and the trail of the offenders could easily be irretrievably lost.
The collective knowledge doctrine also suggests that the personal knowledge of the affiant is irrelevant when the source of the hearsay was another officer. Pursuant to this doctrine, the knowledge of other investigating officers is imputed to the affiant. The Supreme Court of Delaware indicated in State v. Cooley that when officers have been in communication with one another, “the collective knowledge of an entire organization may be imputed to an individual officer.” Similarly, the United States Court of Appeals for the Third Circuit, along with other jurisdictions, has indicated that probable cause is to be evaluated on the basis of the collective information of the police. While the collective knowledge doctrine only applies when the officers have been in communication, the Court can infer communication in this case between the hearsay declarant officers and the affiants, as the declarant officers’ specific observations are contained in the affidavit prepared by the affiants.