Chain of Custody in Drug Cases: Why Marking Evidence Matters

In illegal drug cases, the prohibited substance itself is the very heart of the prosecution's case. If the identity of that substance cannot be proven with certainty, the case falls apart. In Lopez v. People (G.R. No. 184037, September 29, 2009), the Supreme Court reminded law enforcers and prosecutors of this fundamental rule when it acquitted a man convicted of illegal possession of shabu because the police failed to properly establish the chain of custody of the seized drug.

The Facts of the Case

In the early morning of April 23, 2003, Police Officer 2 Apolinario Atienza was on foot patrol in Mandaluyong City when he saw Antonio Lopez walking toward him, head bowed, holding a plastic sachet containing a crystalline substance. PO2 Atienza approached, held Lopez's hand, and asked, "Ano yan?" (What is that?). Lopez did not answer. The officer then arrested him, confiscated the sachet, and brought him to the police station.

At the station, PO2 Atienza prepared a request for laboratory examination and placed his initials "APA" on the plastic sachet. The Chemistry Report later confirmed the contents as methamphetamine hydrochloride, or shabu. The trial court convicted Lopez, and the Court of Appeals affirmed, relying on the arresting officer's testimony and the presumption of regularity in police work.

The Issue

The core question before the Supreme Court was whether the prosecution had proven beyond reasonable doubt that the drug presented in court was the same one seized from Lopez. Specifically, the Court examined whether the police complied with the chain of custody requirements under Section 21 of Republic Act No. 9165, the Comprehensive Dangerous Drugs Act of 2002.

The Chain of Custody Rule

The Supreme Court explained that in drug prosecutions, the narcotic substance itself constitutes the corpus delicti—the body of the crime. Its existence and identity must be established beyond reasonable doubt. The chain of custody rule serves this function: it ensures that the drug offered in court is the same one seized from the accused, with no opportunity for tampering or substitution.

Every person who handles the evidence must testify about how and from whom they received it, what happened to it while in their possession, and the precautions taken to preserve its integrity. This testimony creates a reliable assurance that the evidence is authentic.

The Fatal Flaw: Marking Outside the Accused's Presence

In this case, the prosecution's evidence fell short. PO2 Atienza testified that he confiscated the sachet and brought it to his office. Only then—at the police station, not at the scene—did he place his initials on the plastic sachet. The prosecution also failed to prove that Lopez was present when the marking was done.

The Court emphasized that the law requires the seized drug to be marked in the presence of the accused. This is not a mere technicality. Marking at the scene and in the accused's presence prevents switching, planting, or contamination of evidence. Its absence casts doubt on the identity of the corpus delicti and undermines the claim of regularity in the police operation.

The Presumption of Regularity Cannot Save the Case

The lower courts relied heavily on the presumption of regularity in the performance of official duties. The Supreme Court clarified that this presumption only arises when there are no contradicting details that raise doubts about the regularity of official conduct. Where police officers fail to follow the standard procedure prescribed by law, the presumption has no place.

Because the identity of the drug was not proven beyond reasonable doubt, the Court reversed the conviction and acquitted Lopez.

Practical Takeaways

• Mark evidence immediately at the scene. The marking of seized drugs should be done right after seizure, in the presence of the accused, not later at the police station.
• Document every link in the chain. Each person who handles the evidence must be presented in court to testify about their receipt, custody, and transfer of the item.
• Comply with Section 21 of RA 9165. The physical inventory and photographing of seized drugs must be done in the presence of the accused (or their representative), a media representative, a DOJ representative, and an elected public official.
• Presumption of regularity is not automatic. Courts will not presume regularity when police officers deviate from established procedures without justifiable grounds.
• For the accused, scrutinize the evidence chain. A break in the chain of custody can be the strongest defense in a drug case, even when the substance tests positive for a dangerous drug.

This article is general information and not legal advice. For your specific situation, consult a lawyer or ask ASG Legal AI.