On 31.08.2020, a Constitution Bench of the Supreme Court delivered its unanimous verdict in Mukesh Singh v. State (Narcotic Branch of Delhi) [SLP (Crl.) Diary No. 39528/2018 decided on 31.08.2020, along with other batch matters]. The Constitution Bench had been assembled to decide on the correctness of a Three Justices' Bench decision of 2018, Mohan Lal [AIR 2018 SC 3853].
"On considering the entire decision of this Court in the case of Mohan Lal (supra), it appears that in this case also the Court did not consider in detail the relevant provisions of the Cr.P.C. under which the investigation can be undertaken by the investigating officer, more particularly Sections 154, 156 and 157 and the other provisions, namely, Section 465 Cr.P.C. and Section 114 of the Indian Evidence Act. Even in the said decision, this Court did not consider the aspect of prejudice to be established and proved by the accused in case the investigation has been carried out by the informant/complainant, who will be 35 one of the witnesses to be examined on behalf of the prosecution to prove the case against the accused. This Court also did not consider in detail and/or misconstrued both the scheme of the NDPS Act and the principle of reverse burden."
... Only in a case where the accused has been able to establish and prove the bias and/or unfair investigation by the informant-cum investigator and the case of the prosecution is merely based upon the deposition of the informant-cum-investigator, meaning thereby prosecution does not rely upon other witnesses, more particularly the independent witnesses, in that case, where the complainant himself had conducted the investigation, such aspect of the matter can certainly be given due weightage while assessing the evidence on record. Therefore, as rightly observed by this Court in the case of Bhaskar Ramappa Madar (supra), the matter has to be decided on a case to case basis without any universal generalisation. As rightly held by this Court in the case of V. Jayapaul (supra), there is no bar against the informant police officer to investigate the case. As rightly observed, if at all, such investigation could only be assailed on the ground of bias or real likelihood of bias on the part of the investigating officer the question of bias would depend on the facts and circumstances of each case and therefore it is not proper to lay down a broad and unqualified proposition that in every case where the police officer who registered the case by lodging the first information, conducts the investigation that itself had caused prejudice to the accused and thereby it vitiates the entire prosecution case and the accused is entitled to acquittal. (Emphasis supplied)