Prinsip berkaitan peranan sumber pernah dibincangkan oleh Mahkamah Rayuan dalam kes Heng Poh Kean v. PP & other appeals [2019] 9 CLJ 69 yang telah merujuk kepada kedua-dua nas di atas dan Mahkamah Rayuan menyatakan seperti berikut: “Role Of The Informer [10] The law relating to an informer is settled. Under s. of the DDA, the identity of an informer is protected from disclosure in any legal proceedings, which necessarily S/N xEqxjA3le0OxQLb/VkPawg includes protection from being identified and called to testify in a criminal trial. [11] However, it was submitted before us by learned counsel for the second appellant and adopted by counsels for the first and third appellants, that the informer in this case had assumed the role or mantle of an agent provocateur. Therefore, it was argued that the identity of the informer lost its protection under the law. The informer in fact has metamorphosed into an essential witness for the prosecution and the failure on the part of the prosecution to call the informer to testify had seriously compromised its case, warranting the adverse inference under s. 114 illustration (g) of the Evidence Act 1950, against the prosecution to be invoked. [12] In support of his submission, learned counsel relied on the judgment of the Federal Court in Wan Yurillhami Wan Yaacob & Anor v. PP [2010] 1 CLJ 17; where it was held that: [16] From the decision of the above cited cases, the position in law in relation to s. 40 and 40A of the Act is well settled and clear. The informer is protected from giving evidence whilst an agent provocateur is not protected. In other words, if a person is only an informer, the prosecution is not required to call him as a witness or offering him to the defence. An informer is protected under S/N xEqxjA3le0OxQLb/VkPawg s. 40 of the Act. On the other hand, if a person is an agent provocateur, he is required to give evidence in court as a prosecution witness and if he is not called he has to be offered and made available to the defence. Failure to comply with this requirement will attract the application of adverse inference under s. 114(g) of the Evidence Act against the prosecution's case. [13] The guiding principle regarding the issue can further be found in the Federal Court case of Ti Chuee Hiang v. Public Prosecutor [1995] 3 CLJ 1; in which it was laid down as follows: Having said that, it is in our view clear law, that while the prosecution has a complete discretion as to the choice of witnesses to be called at the trial (see eg, Adel Muhammed el Dabbah v. AG (Palestine) [1994] AC 156 at 167-9) the most basic limitation upon prosecutorial discretion in the presentation of a case, is that it also has a duty to call all of the necessary witnesses to establish proof against the accused beyond all reasonable doubt, and if, in the exercise of its discretion, it fails to fulfil this obligation which is nothing less than a statutory duty - the accused must be acquitted. In the present case, the informer, having regard to his role, was not a mere informer, but had assumed the mantle of an agent provocateur, for it was he, who had put the S/N xEqxjA3le0OxQLb/VkPawg appellant in touch with the undercover agent Lian. Indeed, he was the active instrument without whose intervention, the appellant might never have been even arrested. His identity was no longer a secret and thus he had lost the protection from disclosure of identity normally accorded to informers under s. 40 of the Act. In these circumstances, he came within the category of witnesses, described by Lord Roche in Seneviratne, as "witnesses essential to the unfolding of the narratives on which the prosecution case is based." The same might be said of the informer's friend. Yet, neither the so called informer nor his friend, whose testimony would have been essential to the unfolding of the narrative on which the prosecution case was based, was called by the prosecution or even made available to the defence to be called as defence witnesses nor any explanation vouchsafed to the trial Judge for these glaring omissions. We hasten to add, that in a case such as the present, where it was never suggested by the prosecution that either of these individuals was not capable of belief, it would not have sufficed for the prosecution to have merely made them available to the defence to be called as defence witnesses as such a course would have put the defence to the disadvantage of not having been able to cross-examine them on any point on which they might support the prosecution case. S/N xEqxjA3le0OxQLb/VkPawg In our view, having regard to the circumstances of the present case, it was the obligation of the prosecution to call and examine these individuals as their witnesses or, at least, to have offered them for cross-examination by the defence or in default to have explained why they were unable or unwilling to call them as the case may be. We say so because without their testimony there was a gap in the narrative of the prosecution case. Moreover, there was no suggestion that their testimony would have been obviously hostile to the prosecution or otherwise unreliable, in which case, "the prosecutor will ensure that the accused is given the opportunity to call the witness". (Per the High Court of Australia in Richardson, ibid). [14] The pertinent question thus is whether the informer in this case had in fact assumed the mantle of an agent provocateur and hence became "witnesses essential to the unfolding of the narratives on which the prosecution case is based?”