A landmark judgment by a Full Bench of Supreme Court of India around the question,

From Para 9,

whether, after a charge-sheet is filed by the police, the Magistrate has the power to order further investigation, and if so, up to what stage of a criminal proceeding.

From Para 25,

25. Whereas it is true that Section 156(3) remains unchanged even after the 1973 Code has been brought into force, yet the 1973 Code has one very important addition, namely, Section 173(8), which did not exist under the 1898 Code. As we have noticed earlier in this judgment, Section 2(h) of the 1973 Criminal Procedure Code defines “investigation” in the same terms as the earlier definition contained in Section 2(l) of the 1898 Criminal Procedure Code with this difference – that “investigation” after the 1973 Code has come into force will now include all the proceedings under the CrPC for collection of evidence conducted by a police officer. “All” would clearly include proceedings under Section 173(8) as well. Thus, when Section 156(3) states that a Magistrate empowered under Section 190 may order “such an investigation”, such Magistrate may also order further investigation under Section 173(8), regard being had to the definition of “investigation” contained in Section 2(h).

From Para 36,

36. Despite the aforesaid judgments, some discordant notes were sounded in three recent judgments. In Amrutbhai Shambubhai Patel v. Sumanbhai Kantibai Patel (2017) 4 SCC 177, on the facts in that case, the Appellant/Informant therein sought a direction under Section 173(8) from the Trial Court for further investigation by the police long after charges were framed against the Respondents at the culminating stages of the trial. The Court in its ultimate conclusion was correct, in that, once the trial begins with the framing of charges, the stage of investigation or inquiry into the offence is over, as a result of which no further investigation into the offence should be ordered. But instead of resting its judgment on this simple fact, this Court from paragraphs 29 to 34 resuscitated some of the earlier judgments of this Court, in which a view was taken that no further investigation could be ordered by the Magistrate in cases where, after cognizance is taken, the accused had appeared in pursuance of process being issued. In particular, Devarapalli Lakshminarayana Reddy (supra) was strongly relied upon by the Court. We have already seen how this judgment was rendered without adverting to the definition of “investigation” in Section 2(h) of the CrPC, and cannot therefore be relied upon as laying down the law on this aspect correctly.

From Para 38,

38. There is no good reason given by the Court in these decisions as to why a Magistrate’s powers to order further investigation would suddenly cease upon process being issued, and an accused appearing before the Magistrate, while concomitantly, the power of the police to further investigate the offence continues right till the stage the trial commences. Such a view would not accord with the earlier judgments of this Court, in particular, Sakiri (supra), Samaj Parivartan Samudaya (supra), Vinay Tyagi (supra), and Hardeep Singh (supra); Hardeep Singh (supra) having clearly held that a criminal trial does not begin after cognizance is taken, but only after charges are framed. What is not given any importance at all in the recent judgments of this Court is Article 21 of the Constitution and the fact that the Article demands no less than a fair and just investigation. To say that a fair and just investigation would lead to the conclusion that the police retain the power, subject, of course, to the Magistrate’s nod under Section 173(8) to further investigate an offence till charges are framed, but that the supervisory jurisdiction of the Magistrate suddenly ceases mid-way through the pre-trial proceedings, would amount to a travesty of justice, as certain cases may cry out for further investigation so that an innocent person is not wrongly arraigned as an accused or that a prima facie guilty person is not so left out. There is no warrant for such a narrow and restrictive view of the powers of the Magistrate, particularly when such powers are traceable to Section 156(3) read with Section 156(1), Section 2(h), and Section 173(8) of the CrPC, as has been noticed hereinabove, and would be available at all stages of the progress of a criminal case before the trial actually commences. It would also be in the interest of justice that this power be exercised suo motu by the Magistrate himself, depending on the facts of each case. Whether further investigation should or should not be ordered is within the discretion of the learned Magistrate who will exercise such discretion on the facts of each case and in accordance with law. If, for example, fresh facts come to light which would lead to inculpating or exculpating certain persons, arriving at the truth and doing substantial justice in a criminal case are more important than avoiding further delay being caused in concluding the criminal proceeding, as was held in Hasanbhai Valibhai Qureshi (supra). Therefore, to the extent that the judgments in Amrutbhai Shambubhai Patel (supra), Athul Rao (supra) and Bikash Ranjan Rout (supra) have held to the contrary, they stand overruled. Needless to add, Randhir Singh Rana v. State (Delhi Administration) (1997) 1 SCC 361 and Reeta Nag v. State of West Bengal and Ors. (2009) 9 SCC 129 also stand overruled.

From Para 43,

43. We, therefore, set aside the impugned High Court judgment insofar as it states that post-cognizance the Magistrate is denuded of power to order further investigation.

Citations : [2019 SCC ONLINE SC 1346], [(2019) 17 SCC 1], [AIR 2019 SC 5233], [2020(1) R.C.R. (Criminal) 1], [(2019) 14 SCALE 1]

Other Sources :

https://indiankanoon.org/doc/131202146/

https://www.casemine.com/judgement/in/5da99d013321bc410549721e

https://www.indianemployees.com/judgments/details/vinubhai-haribhai-malaviya-and-ors-versus-the-state-of-gujarat-and-anr