Members of the Garda Siochana sometimes get confidential information from informants. Frequently neither the informant nor the Garda wish the source of the information to emerge publicly.
Its emergence can be prevented under the common law âinformer privilegeâ?.
Generally the information will lead to an application for a search warrant. The application is generally made to a District Court judge or, sometimes, a Peace Commissioner.
The Garda applicant will usually have to prove on oath that s/he has reasonable grounds for believing [a set of facts] indicating the need for a search of a premises. The judge or Commissioner might ask questions and would, in the event of receiving unsatisfactory replies, be in a position to decline to issue the warrant.
Generally, therefore, there is some safeguard against abuse by the Garda Siochana.
If the warrant is not validly issued the lawfulness of the search and the admissibliity of any evidence obtained will be compromised.
In DPP v Yamanoha  1 IR p. 565 the Garda Siochana applied to a Peace Commissioner for a search warrant for a search of an hotel room. The record of the facts sworn to, showed the officer said he was a Garda officer and held a belief. The grounds of the belief were recited as confidential information and surveillance by other officers. The validity of the warrant was challenged on the basis that the Peace Commissioner had no knowledge of the statutory grounds for the issue of the warrant. The prosecution led further evidence, of the giving of oral evidence, given by the Garda officer to the Peace Commissioner. Unfortunately, the Peace Commissioner remembered this as being tendered before the officer took the oath; the officer remembered it as being tendered afterwards. The trial judge accepted the evidence of the officer but the Court of Criminal Appeal quashed the conviction [for possession of drugs] deeming the warrant invalid, remarking that the trial judge should have preferred the evidence of the Peace Commissioner.
In Hanahoe & Ors. v Hussey & Ors.  3 IR p. 69 a district Court judge issued a search warrant on the averment of a Garda officer that he had reasonable ground for suspicionâ¦ The High Court found, inter alia, that the officer was, in applying for the warrant, obliged to justify the officerâs opinion by revealing the relevant facts to the judge being asked to issue the warrant.
In The People (DPP) v Mark Kenny  2 IR p. 110 the Court of Criminal Appeal held that a warrant issued by a Peace Commissioner on the basis of Garda evidence that the Garda had âa suspicionâ? pursuant to information in his possession was invalid. The Peace Commissioner was the person to be satisfied and an inquiry into the basis for the Gardaâs belief was obligatory. Nevertheless, the CCA declared the evidence obtained pursuant to the warrant admissible. The Supreme Court, on appeal, found that evidence obtained as a result of a deliberate and conscious violation of constitutional rights of a citizen must be excluded unless the court in its discretion was satisfied that there were extraordinary excusing circumstances which justified the admisison of the evidence or that the act constituting the breach of constitutional rights was committed unintentionally or accidentally. In the particular case there were no extraordinary excusing circumstances and the act was not committed unintentionally or accidentally and therefore the evidence was not admissible.
Whatever about the relative safeguard of the need to apply to a District Court judge or a Peace Commissioner for a warrant, there can be very little where the warrant is issued under the provisions of Section 29 of the Offences Against the State Act 1939 as inserted by Section 5 of the Criminal Law Act 1976. In that case the issuing authority is another Garda officer not below the rank of superintendent. There is no obligation that the superintendent be operationally divorced from the applicant officer.
In other words, the police issue the search warrant to the police.
Furthermore, “informants” may be Garda officers, sometimes the applicant officer himself.
The opportunity to challenge the “confidentiality” of the basis of the application will be reduced to nil.