Mukesh Singh v. State (Narcotic Branch of Delhi)

In Mohan Lal v. State of Punjab (2018) 17 SCC 627, a three-Judge Bench of the Supreme Court held that in criminal prosecutions—especially under the stringent provisions of the Narcotic Drugs and Psychotropic Substances Act, 1985 (NDPS Act)—a fair trial and fair investigation under Article 21 require that the person who lodges the complaint or FIR (the informant) cannot investigate the case. Mohan Lal laid down a sweeping blanket rule: if the informant conducts the investigation, the trial is automatically vitiated and the accused is entitled to an automatic acquittal.

This ruling triggered widespread legal upheaval across trial courts and High Courts nationwide. Thousands of pending NDPS prosecutions where seizing officers had investigated recovery operations collapsed. Soon thereafter, in Varinder Kumar v. State of Himachal Pradesh (2020) 3 SCC 321, another three-Judge Bench held that Mohan Lal would operate only prospectively. However, earlier binding precedents—including State v. V. Jayapaul (2004) 5 SCC 223, S. Jeevanantham v. State (2004) 5 SCC 230, and Bhaskar Ramchandran Sonawane v. State of Maharashtra (2009) 16 SCC 648—had consistently held that there is no statutory bar against an informant investigating the case unless actual prejudice or bias is established.

Doubting the correctness of Mohan Lal, a Division Bench and subsequently a three-Judge Bench referred the question to a 5-Judge Constitution Bench in Mukesh Singh v. State (Narcotic Branch of Delhi) to conclusively determine whether an informant investigating the offence automatically invalidates the prosecution.

1. Legality of Informant as Investigator: Whether in a criminal prosecution (particularly under the NDPS Act or under general criminal law), the trial is automatically vitiated and the accused entitled to acquittal if the investigation is conducted by the police officer who himself is the complainant/informant?
2. Correctness of Mohan Lal v. State of Punjab: Whether the three-Judge Bench in Mohan Lal (2018) correctly laid down the law by holding that fair trial under Article 21 is inherently compromised whenever the informant investigates the case?
3. Presumption of Bias vs. Proof of Prejudice: Does the dual capacity of an officer as informant and investigating officer raise a presumption of bias as a matter of law, or must actual bias/prejudice be established by the accused on a case-to-case basis?
4. Statutory Scheme of NDPS Act: Whether Sections 41, 42, 43, 52, 53, and 53A of the NDPS Act permit an authorized officer who detects, seizes, or arrests to carry forward the investigation?

Authoring the unanimous verdict for the 5-Judge Constitution Bench, Justice M.R. Shah laid down the definitive legal framework governing the investigating officer's status:

A. No Statutory Bar Under CrPC or NDPS Act

The Constitution Bench closely examined the provisions of Chapter XII of the Code of Criminal Procedure, 1973 (Sections 154, 156, 157, and 173) and Sections 41, 42, 43, 52, and 53 of the NDPS Act. The Court held that there is NO statutory prohibition against an informant investigating the crime:

"In a case where the informant himself is the investigating officer, by that itself cannot be said that the investigation is vitiated on the ground of bias or the like factor. The question of bias or prejudice would depend upon the facts and circumstances of each case. Therefore, merely because the informant is the investigating officer, by that itself the investigation would not suffer from the vice of lack of fairness or impartiality."

B. Express Overruling of Mohan Lal (2018)

The Constitution Bench formally overruled Mohan Lal v. State of Punjab, holding that its rigid blanket rule was legally unsound, contrary to the statutory scheme of both the CrPC and the NDPS Act, and failed to consider earlier coordinate bench rulings:

"We are of the opinion that the decision of this Court in the case of Mohan Lal (supra) taking the view that in every case where the informant himself is the investigating officer, by that itself the trial would be vitiated and the accused would be entitled to an acquittal cannot be said to be laying down the correct law. The decision in the case of Mohan Lal is hereby overruled."

C. The Burden of Proving Bias Rests on the Accused

The Court settled that bias cannot be assumed in the abstract. An accused seeking an acquittal on the ground that the informant acted as the investigating officer must establish actual bias, prejudice, malice, or extraneous considerations during the trial. In the absence of proof of prejudice, the evidence collected by the officer and corroborated by other witnesses cannot be discarded.

D. Operational Reality of NDPS Enforcement

The Bench noted that police officers or narcotics enforcement officials who receive secret intelligence, lay ambushes, and intercept contraband carriers under Section 42 or 43 of the NDPS Act are duty-bound to draw seizure memos and take custody. To hold that the seizing officer cannot investigate would lead to administrative paralysis, where an officer unfamiliar with the spot investigation would have to be mechanically substituted without functional necessity.

The Constitution Bench reviewed decades of conflicting Supreme Court authorities:

• State v. V. Jayapaul (2004) 5 SCC 223: Reaffirmed that there is no principle of law that a police officer who is the complainant is disqualified from conducting the investigation. The head of police or the investigator is not an interested witness merely by reason of being an enforcement official.
• S. Jeevanantham v. State (2004) 5 SCC 230: Endorsed the view that in the absence of any prejudice shown to have been caused to the accused, the prosecution cannot be thrown out solely because the complainant also investigated.
• Babu Bhai v. State of Gujarat (2010) 12 SCC 254: Reconciled the requirement of fair and impartial investigation under Article 21, affirming that while a biased investigation violates fundamental rights, bias must be demonstrated from concrete material, not presumed from official roles.
• Varinder Kumar v. State of Himachal Pradesh (2020) 3 SCC 321: The transitional ruling which had made Mohan Lal prospective was rendered academic following the outright overruling of Mohan Lal in Mukesh Singh.

How the principles in Mukesh Singh map across India's new criminal procedural framework: