A public entity has a privilege to refuse to disclose the identity of a person who has furnished information purporting to disclose a violation of a law of the Commonwealth of Puerto Rico or of the United States of America if the information is furnished in confidence by the informer to a law enforcement officer, a representative of the administrative agency charged with the administration or enforcement of the law alleged to be violated, or any person for the purpose of transmitting it to such officer or representative. Evidence of informer’s identity is not admissible unless the court determines that it has already been disclosed in any other way, or that information on his identity is essential for the administration of even-handed justice, particularly where such information is essential to the defense of the accused.