Note: This is general legal information written for the Philippine context and does not create a lawyer-client relationship.

1) Snapshot: What a “buy-bust” case looks like

A buy-bust is a form of entrapment where law-enforcement (often PDEA or police) uses an undercover “poseur-buyer” to purchase drugs and arrest the seller in flagrante delicto (caught in the act). Cases commonly filed include:

Sale of dangerous drugs (Sec. 5, R.A. 9165)
Possession (Sec. 11) and paraphernalia (Sec. 12), often as companion charges
Use (Sec. 15), depending on facts

While entrapment is lawful, instigation is not. Instigation happens when officers originate the criminal design and induce a person who had no prior intent to commit the crime; it is a complete defense. The Supreme Court’s “objective test” in People v. Doria (1999) examines the details of the transaction—how the buy was set up, who initiated it, and how the exchange unfolded.

2) Governing law, rules, and landmark doctrines

R.A. 9165 (Comprehensive Dangerous Drugs Act of 2002) and R.A. 10640 (2014 amendment to Sec. 21 on chain of custody)
Rules of Court (esp. Rule 113 on arrests; Rule 117 on quashal; Rule 115 on rights of accused; Rule 119 on speedy trial & demurrer; Rule 121 on new trial)
Bill of Rights, 1987 Constitution (arrest/search, custodial investigation, exclusionary rule)
R.A. 7438 (rights of persons arrested/detained) & Art. 125, Revised Penal Code (delivery to proper judicial authorities)
Plea bargaining: Estipona v. Lobrigo (2017) struck down the plea-bargaining ban; the Court later issued the Plea Bargaining Framework in Drugs Cases (A.M. No. 18-03-16-SC).
Chain-of-custody jurisprudence: People v. Malillin (2008), People v. Umipang (2012), People v. Lim (2018) (State must justify any Sec. 21 deviation), People v. Sipin (2018), among others.
On presumptions: People v. Mendoza (2014) – presumption of regularity cannot by itself overcome presumption of innocence.

3) Validity of the arrest and search

A. Warrantless arrest theory

Buy-bust arrests are typically justified under Rule 113, Sec. 5(a): a person is arrested when actually committing an offense (in flagrante delicto). Officers must testify to overt acts showing a real-time offense (e.g., handing over sachets for marked money), not merely a confidential tip.

B. Search incident to a lawful arrest

After a lawful arrest, officers may conduct a search of the person and immediate surroundings. Items seized are admissible if the arrest is valid and the search stays within proper bounds. If the arrest is invalid, the search is likewise unlawful, and the evidence is excluded under Art. III, Sec. 3(2) (exclusionary rule).

Remedy: Challenge the arrest (Rule 113) and move to suppress evidence seized as a consequence of an illegal arrest/search. Object before arraignment; otherwise, defects in the manner of arrest are generally waived, although illegal search and seizure (a constitutional violation) may still be a basis for suppression.

4) Chain of custody: the pivot of most defenses

A. What Sec. 21 requires (as amended by R.A. 10640)

Immediate marking of seized items by the apprehending officer
Physical inventory and photographs of the items immediately after seizure and confiscation
In the presence of the accused or representative and required witnesses:
- One elected public official, and
- A representative of the National Prosecution Service (NPS) or the media
Conducted at the place of seizure or, if not practicable, at the nearest police station/office
Proper turnover, storage, and laboratory examination; the forensic chemist and seizing officer(s) should link each step.

B. The “saving clause”

Per People v. Lim, the State must (i) recognize any noncompliance, (ii) offer specific, credible reasons for it, and (iii) still prove preservation of integrity and evidentiary value. A generic “substantial compliance” claim is insufficient. Courts often acquit when:

Marking was not immediate or was done by someone other than the seizing officer without explanation
Required witnesses were absent without valid reason or were invited after the inventory/photography
Gaps exist in custody (who handled the item, when, and how)
The poseur-buyer or forensic chemist is not presented, leaving identity of the corpus delicti in doubt

Remedies:

Pre-trial/Trial: Move to suppress the seized drug for Sec. 21 lapses; vigorously cross-examine to expose chain breaks; insist on presenting poseur-buyer, seizing officer, evidence custodian, and forensic chemist.
Post-judgment: Argue reasonable doubt from chain-of-custody defects on appeal.

5) Entrapment vs. instigation

Entrapment (lawful): Officers merely provide an opportunity to commit an offense to catch a person already minded to commit it.
Instigation (unlawful): The criminal design originates with the police, who lure an otherwise innocent person into committing a crime; it absolves the accused.

Remedies: Raise instigation as a substantive defense; use detailed cross-examination to show who initiated contact, who proposed the sale, and whether the accused had prior intent.

6) Rights from arrest through inquest and arraignment

A. Upon arrest (Constitution; R.A. 7438)

Be informed in a language known to the person of the cause of arrest and rights
Counsel during custodial interrogation (or one provided)
Silence; statements without counsel are inadmissible
To communicate with family and counsel; to have visitation rights

Remedies: Suppress any extra-judicial confession taken without counsel, or obtained through coercion.

B. Inquest and Art. 125 RPC

Warrantless arrests must be inquested by a prosecutor within strict time limits (generally up to 36 hours for serious offenses).
The arrested may waive inquest and request preliminary investigation, but the waiver must be in writing and in counsel’s presence.

Remedies: If held beyond Art. 125 periods without proper processing, consider criminal/administrative action against responsible officers and seek immediate release if no complaint/information is filed.

C. Bail

As a matter of right for offenses not punishable by reclusion perpetua/life.
Discretionary (and may be denied) when the charge is punishable by life imprisonment (e.g., sale under Sec. 5, large-quantity possession), if the evidence of guilt is strong.
Court must conduct a bail hearing where the prosecution bears the burden to show that evidence of guilt is strong.

7) Remedies and defenses by stage

A. Before arraignment

Motion to quash the Information (e.g., facts do not constitute an offense; lack of authority of officer; duplicitous charge; void Information)
Motion to suppress: (i) illegal arrest/search; (ii) Sec. 21 chain defects; (iii) uncounselled admissions
Motion for reinvestigation (if filed without preliminary investigation or with material lapses)
Petition for habeas corpus for unlawful detention without valid charge

B. Pre-trial & trial

Move to exclude: marked money or buy-bust items lacking proper identification; lab results absent proof of unbroken chain
Cross-examine on the objective test (Doria): who initiated, where, how the buy was arranged, presence of pre-operation and post-operation reports, use of marked money, surveillance, and independent witnesses
Object to hearsay and conclusory testimonies (“we received a tip…”) where offered for the truth
Demurrer to evidence (with or without leave) after the prosecution rests, if the evidence fails on elements or chain of custody
Partial demurrer where multiple counts/charges exist

C. Plea bargaining in drugs cases

After Estipona, plea bargaining is allowed subject to the Supreme Court’s framework (A.M. No. 18-03-16-SC).
Courts consider: the quantity/penalty, criminal history, opposition by the prosecutor (grounded on valid reasons), drug dependency assessment, and compliance with rehabilitative conditions.
A carefully timed plea may reduce exposure where evidence is technically adequate but not overwhelming.

D. Speedy trial & provisional dismissal

Assert speedy trial (Const., Rule 119; Speedy Trial Act) when delays are unjustified and prejudicial.
Provisional dismissal (Rule 117, Sec. 8) with the accused’s consent and notice to the offended party can ripen into permanent dismissal if not revived within statutory periods.

E. Judgment and post-judgment

Motion for reconsideration or new trial (Rule 121), e.g., newly discovered evidence; significant procedural error
Appeal to the Court of Appeals; then Rule 45 to the Supreme Court on questions of law
Rule 65 extraordinary writs (grave abuse of discretion) in exceptional circumstances
Bail pending appeal (discretionary; rarely granted in life-imprisonment cases)

F. Civil and administrative recourse

Civil action for damages (Civil Code Arts. 19, 20, 21) for illegal arrest, coercion, or rights violations
Administrative complaints vs. officers (e.g., PLEB, NAPOLCOM, IAS, Ombudsman)
Assistance/complaints before the Commission on Human Rights

8) Elements and proof—what the prosecution must establish

A. Sale (Sec. 5)

Identity of the buyer/seller
Object of the sale (the drug)
Consideration (marked money)
Delivery of the thing sold and payment
Corpus delicti: same item from seizure to lab to court (chain of custody)

Common attack points: No pre-arranged signal; marked money not presented; poseur-buyer not presented; discrepancy in descriptions (weight, packaging, markings); late marking; inventory defects; missing witnesses.

B. Possession (Sec. 11)

Possession or control (actual or constructive)
Knowledge of possession
Object is a dangerous drug
Chain of custody of the item presented in court

Common attack points: Mere presence at scene; items found in shared spaces; lack of exclusive control; planted evidence theory supported by inconsistencies and absence of independent witnesses.

9) Evidence-handling checklist for the defense

Was marking done immediately by the apprehending officer who seized the item?
Where and when were inventory and photos taken—on-site or at the nearest station—and who witnessed them?
Were the required witnesses (elected official + NPS/media) present during inventory/photography? If absent, what specific, credible reasons exist?
Is there a continuous, documented chain from seizure → inventory → temporary custodian → forensic lab → evidence custodian → in-court presentation?
Did the poseur-buyer testify and identify the accused and the item?
Did the forensic chemist personally handle and seal the item, and are the laboratory numbers consistent?
Are there discrepancies in weight/packaging/markings between seizure, lab, and trial?

10) Procedural defenses and pitfalls

Timely objections are critical. Suppression issues must be raised at the earliest opportunity, typically before arraignment.
Entering a plea generally waives defects in the manner of arrest, but not constitutional objections to illegally seized evidence.
Non-presentation of essential witnesses (poseur-buyer; forensic chemist) can be fatal where identity of the corpus delicti or transaction becomes doubtful.
The presumption of regularity does not substitute for proof beyond reasonable doubt, especially amid Sec. 21 lapses.

11) Strategic pathways (high-level)

Early case audit: Scrutinize arrest narrative, body-cam/phone videos if any, blotter, pre-/post-ops reports, inventory/photos, and witness availability.
Front-load suppression: Illegal arrest/search and Sec. 21 defects can knock out the corpus delicti.
Build the instigation theory where facts support it; highlight who initiated the buy and how aggressively.
Protect the record: Make specific objections; ask the court to note unavailability of required witnesses; request subpoenas promptly.
Plea-bargain windows: Consider after bail/prosecution evidence evaluation, consistent with the SC framework and client’s risk tolerance.
Speedy-trial pressure: Track delays; file time-bound motions; consider provisional dismissal where appropriate.
Appellate posture: Preserve issues of law (admissibility; constitutional violations; Sec. 21 compliance) and fact (credibility; chain gaps) for CA/SC review.

12) Mini-templates (issue framing)

Motion to Suppress (Illegal Search/Seizure): “Accused respectfully moves to suppress all items seized and their fruits, the arrest and search being unlawful, there being no valid in-flagrante justification under Rule 113, Sec. 5(a) and, alternatively, the search exceeding the limits of a valid search incident to arrest. The seized items are thus inadmissible under Art. III, Sec. 3(2) of the Constitution.”
Motion to Suppress (Sec. 21 Lapses): “The prosecution failed to prove an unbroken chain of custody. Marking was not immediate; the required witnesses were absent during inventory and photography without credible justification; and material breaks exist between seizure, laboratory handling, and court presentation. Under People v. Lim and related cases, these lapses generate reasonable doubt as to the identity and integrity of the corpus delicti.”
Petition for Bail (Non-bailable Charge): “Accused prays for bail and an immediate hearing. The prosecution bears the burden to show that the evidence of guilt is strong. On the face of its evidence—marked-money mismatch, absent poseur-buyer, and Sec. 21 irregularities—this burden cannot be met.”
Motion to Dismiss for Speedy-Trial Violation: “Repeated, unjustified postponements attributable to the prosecution over a prolonged period have caused prejudice to the defense (witness unavailability; anxiety; incarceration). Under constitutional and statutory speedy-trial guarantees, dismissal with prejudice is warranted.”

13) Quick reference: common prosecution weaknesses

Confidential tip alone used to justify arrest (no overt act)
No marked money or failure to present it
Poseur-buyer or forensic chemist not presented
Late or unclear marking; inventory photos taken without required witnesses
Inconsistent accounts on where inventory occurred or who handled the sachet
Discrepant weights/labels between seizure, lab, and trial
Speculative assertions (“he looks like a pusher”) in place of transaction details
Delays violating speedy-trial standards

14) Closing perspective

Drug buy-bust litigation almost always turns on procedure: the lawfulness of the arrest, the integrity of the search and seizure, and a meticulous chain of custody. The defense that identifies concrete breaks or deviations—and ties them to constitutional and statutory benchmarks—often converts small factual doubts into reasonable doubt. The remedies above, deployed early and precisely, can be outcome-determinative.