delivered the opinion of the Court.
Appellant was charged with three violations of § 29 of the Narcotics Act of Puerto Rico, 24 L.P.R.A. § 974z, consisting in possessing, concealing, transporting, and selling the drug known as heroin. He pleaded not guilty in each of the three counts and at the trial he was represented by two attorneys. He was found guilty in the three counts by unanimous jury verdict.
The transaction which gave rise to the information may be summed up as follows: On November 4, 1960, the informer, Antonio Reyes Ríos, and the undercover agent, Ibraim Mestre Sánchez, approached appellant and the former asked him to sell him some heroin. Appellant said that he did not have the drug on his person, that he had it in another place. The informer gave him $10 to get him two decks or small bags of heroin. Defendant then went to Puerta de Tierra housing project and returned with the heroin about 10 minutes later. The informer and agent Mestre waited for him *674on the street near a car. On his return, appellant placed the two small hags of the drug in question on the rear right fender of the car. The informer took them and handed them to Mestre. Another undercover agent named Juan Santiago Meléndez, who had been asked to cooperate with Reyes and Mestre, was observing the transaction from a distance of about 15 feet.
In the prosecution of the case the two agents, Mestre Sánchez and Santiago Meléndez, were prosecution witnesses. Mestre having made reference to the existence of the informer, the defense requested to be informed the name and address of the latter “in order to duly cross-examine the witness who is on the witness stand [Mestre] and to prepare an adequate defense in this case for the benefit of our client.” Upon questioning by the district attorney, witness Mestre testified that the informer’s name was Antonio Reyes Rios, and when the court asked him for the informer’s address, Mestre answered: “Actually I have no knowledge of that.” Thereupon the judge asked the district attorney whether he knew the address of informer Reyes Ríos and the district attorney answered that he did not.
At the commencement of the defense evidence one of defendant’s attorneys announced that the defense theory would arise from the evidence.
The defendant was the first to testify. He said that he knew informer Antonio Reyes Rios by sight; that in July 1960 he came across him on Pelayo Street of San Juan; that there Reyes Rios offered to sell him a gold chain; that he asked $13 for it; and that he purchased it. Defendant also testified that about two weeks later he saw Reyes Rios again; that the latter asked him $13 more alleging that the chain was worth $20,1 that for that reason they engaged in an *675argument and came to blows; that he saw Reyes Rios again two or three times around there, but no further incidents occurred between them. Defendant also testified that he is not a drug addict and has never been a drug trafficker; that sometimes he works at the piers; that he is not unionized.
The second and last defense witness was Juan F. Casañas, a resident of Puerta de Tierra, who said that he knew defendant since the latter was a child; he said that defendant’s reputation was very good; he denied knowing that defendant was called “El Lambío” and that he (the witness) is a friend of defendant’s parents.
Appellant assigns the commission of only the following error:
“The trial court erred in denying defendant’s request to be furnished with the information necessary to establish the identity of informer Antonio Reyes Rios.”
What is known as the “informer’s privilege” is in reality the Government’s privilege to withhold from disclosure the identity of persons who furnish information of violations of law to the authorities. Roviaro v. United States, 353 U.S. 53, 59 (1957); Scher v. United States, 305 U.S. 251, 254 (1938); In re Quarles and Butler, 158 U.S. 532 (1895); Vogel v. Gruaz, 110 U.S. 311, 316 (1884). The purpose of the privilege is the furtherance and protection of the public interest in fighting crime. The existence of the privilege is a judicial recognition of the obligation of citizens to communicate their knowledge of the commission of crimes to law-enforcement officials and, by preserving their anonymity, encourages them to perform that obligation. Roviaro v. United States, supra, p. 59. Undoubtedly, for that reason the Supreme Court of the United States has said that public policy forbids disclosure of an informer’s identity unless essential to the defense. Scher v. United States, supra. See, also, Segurola v. United States, 16 F.2d 563, 565 (1926); *676Shore v. United States, 49 F.2d 519, 522 (1931); McInes v. United States, 62 F.2d 180 (1932).
Another reason for not disclosing the informer’s identity is a corollary of the first, already stated. The usefulness of the informer having been recognized in the always difficult task of protecting society from the underworld, the need for protecting the informers by not identifying them is also recognized, with the exception already noted when essential to the accused’s defense. It is easy to understand that an identified informer runs personal risk. There have been cases in which identified informers have been murdered. Draper v. United States, 358 U.S. 307 (1959); Brown v. United States, 222 F.2d 293 (1955); Schuster v. City of New York, 154 N.E.2d 534 (1958).
This appears at p. 55 of the record. At p. 64 defendant says that on that occasion Reyes Rios asked him $7 more (instead of $20 as he said before).