Offences against public health and circumstantial evidence: requirements for a conviction and the main grounds for nullity that can be raised in criminal proceedings

Summary. The answer to whether a conviction for an offence against public health (delito contra la salud pública, the Spanish legal category that covers drug trafficking) can rest on circumstantial evidence (prueba indiciaria) is yes: the Tribunal Supremo (Spanish Supreme Court) consistently accepts it, and for the subjective element of the offence (the drug being intended for trafficking) it is the ordinary means of proof. Such a conviction does, however, require that the base facts (hechos-base) be fully proven, that the inference be logical and expressly stated, and that the evidence have been obtained with respect for fundamental rights. That is why the study of circumstantial evidence cannot be separated from the rules on nullity: if the base fact derives from a defective telephone interception or search, the indicium falls away. This article addresses both questions, drawing on the case law held in the firm's database of judicial decisions and on the legislation in force.

I. The issue

Art. 368 CP (Spanish Criminal Code) punishes those who “carry out acts of cultivation, production or trafficking, or otherwise promote, encourage or facilitate the illegal consumption of toxic drugs, narcotics or psychotropic substances, or possess them for those purposes”. It provides for imprisonment of three to six years and a fine of one to three times the value of the drug if the substance causes serious harm to health, and imprisonment of one to three years and a fine of one to two times that value in all other cases. Its second paragraph allows a penalty one degree lower to be imposed “in view of the minor significance of the act and the personal circumstances of the offender”, unless the circumstances set out in arts. 369 bis and 370 are present.

Two features of the offence explain why circumstantial evidence is decisive:

• It is an offence of abstract danger. STSJ Extremadura 1167/2026 (a judgment of the Tribunal Superior de Justicia, the regional High Court of Justice, of Extremadura) makes this point when citing Supreme Court doctrine: drug trafficking harms the protected legal interest in the abstract, but a criminal-law response requires the conduct to place that interest in danger, so mere disobedience is not punished.
• It includes a subjective tendency element: the substance being intended for trafficking. SAP Málaga 2084/2026 (a judgment of the Audiencia Provincial de Málaga, the Málaga Provincial Court) lists it alongside the objective element (acts of production, sale, exchange or any form of trafficking, transport or possession for the purpose of trafficking) and the material object (substances included in the schedules of the international conventions, distinguishing those that cause serious harm to health from those that do not). It adds that, for the offence to be complete, it is enough that the substance has come within the recipient's power of disposal, with no need for physical contact or material possession.

II. Circumstantial evidence: basis and requirements

1. Constitutional basis

The right to the presumption of innocence (art. 24.2 CE, the Spanish Constitution) does not prevent a court from forming its conviction on the basis of circumstantial evidence. STS 797/2017 (a judgment of the Supreme Court), reproduced in STS 286/2023, describes the review the Supreme Court carries out when that right is invoked. It checks whether the conviction rests on:

• incriminating evidence that is sufficient and covers all the essential elements of the offence;
• evidence obtained in accordance with the Constitution, that is, without infringing other fundamental rights, which allows the court to examine the validity of evidence obtained directly or indirectly through constitutional violations and the connection of unlawfulness (conexión de antijuridicidad) between them;
• evidence lawfully taken, in compliance with the right to proceedings with all guarantees; and
• evidence rationally assessed, from which the commission of the offence and the defendant's participation in it can rationally be inferred.

This framework is useful because it places nullity within the sufficiency assessment itself: evidence that fails the second or third filter cannot serve as a base fact.

2. Requirements for circumstantial evidence

The same judgment points out that, in the absence of direct evidence, it is possible to rely on circumstantial, indirect or inferential evidence, provided that the following conditions are met:

“(a) the base fact or facts (indicia) must be fully proven; (b) the facts constituting the offence must be deduced precisely from those base facts; (c) for the reasonableness of the inference to be verifiable, the court must set out the indicia and bring to the surface the reasoning or logical link between the base facts and the consequent facts; and (d) this reasoning must be grounded in the rules of human judgement or common experience.”

STS 3780/2019 adds a point about its nature: it is built on a chain of indicia which on their own would not suffice for a conviction, but whose combined weight leads to certainty as to who committed the offence, something that is accepted because in many cases there is no direct evidence. Citing legal scholarship, it defines it as the linked and unrebutted sum of a series of facts that make it possible to reach the consequent fact through an explicit process of inference, always in terms of “certainty beyond all reasonable doubt”.

Two practical consequences follow from this doctrine:

• Circumstantial evidence does not lower the standard of proof. STS 286/2023, citing STS 91/2014 in a money laundering context, stresses that there is no relaxation of the evidentiary requirements, but rather a different way of proving that is capable of reaching the same degree of objective certainty.
• Review in cassation (casación, the appeal on points of law before the Supreme Court) is confined to the rational structure of the reasoning: the Supreme Court checks that the rules of logic, the maxims of experience and scientific knowledge have been observed, but it does not substitute its own assessment of direct evidence such as witness or expert testimony, provided that the trial court had sufficient and valid incriminating evidence and assessed it reasonably.

III. Application to art. 368 CP

1. Intended for trafficking

STSJ Extremadura 1167/2026 reproduces the doctrine of STS 807/2021, which sets out six rules:

1. The purpose of trafficking (destino al tráfico) is an element of the offence and must be proven by the prosecution, normally through circumstantial evidence, both from the standpoint of the presumption of innocence and from that of subsumption under the offence by means of the “process of inference”.
2. The intended destination of the substance should only be examined if there are relevant indications that the holder is a consumer; if nothing supports this, it must be inferred, according to the basic rules of experience, that the substance was intended for trafficking.
3. Being a consumer does not entirely rule out the purpose of trafficking: the other circumstances are assessed, particularly the quantity.
4. To establish that purpose on the basis of quantity, where there is no act of transfer to third parties, guideline thresholds are used, based on average consumption and on the number of days' supply a consumer usually keeps.
5. Case law has established that the purpose of trafficking must be inferred where the drug seized exceeds a consumer's average five-day supply. For cocaine, an average daily consumption of approximately 1.5 grams is taken, which leads to an inference of trafficking for amounts above 7.5 grams. The quantity is calculated on the drug reduced to purity.
6. The purpose of trafficking may be inferred even if the quantity does not exceed the threshold, on the basis of other indicia.

Point 6 itself lists those indicia, which are summarised in the following table.

The counterpoint is SAP Málaga 3064/2020, which acquitted and reproduces STS 1142/2001: where a small quantity is possessed by someone who uses that substance and there are no other indicia, it will not be possible to establish that it was intended for trafficking; and where the quantity amounts to several grams, that single fact will sometimes leave room for doubt, in which case the defendant would also have to be acquitted. The burden of proving the indicia therefore continues to rest with the prosecution.

2. Perpetration of and participation in acts of trafficking

Acts of trafficking usually take place covertly or clandestinely, and it is circumstantial evidence which, drawing on the rules of logic and the maxims of experience, leads to a firm conclusion about the defendants' activity (SAP Málaga 3755/2025, citing the Supreme Court judgment of 31 October 1996). The most common scenarios are:

• Small-scale dealing. STS 2368/2021 dismissed the presumption-of-innocence ground of appeal against a conviction for cocaine trafficking in which no substance had been seized from the defendant. It took into account the testimony of the officers who had twice witnessed the exchange with third parties; that of other officers who stopped the buyers immediately afterwards and seized the doses they had just bought; and the scientific analysis of the substance. It concluded that the inference that the appellant had sold those doses was consistent with logic and the maxims of experience. The same judgment applied the mitigated sub-type of art. 368, second paragraph, and restates the doctrine on it: minor significance exists, among other situations, in the isolated sale of a wrap or two containing a small quantity, “the last rung of trafficking”, and the provision refers to the minor seriousness of the act, not merely to the quantity.
• Organisations. SAP Málaga 2084/2026 convicts the person who led a group on the basis of a proven fact (the cultivation of marijuana for later sale) and of the intercepted telephone conversations, which reveal the instructions given to the other members, the placing of the drug on the market and the planning of purchases and of actions against other groups.
• Coded communications. STS 286/2023 includes, among the proven facts, the use of veiled, cryptic language in intercepted conversations to avoid naming the subject of the dealings. The inference is built on that context.

As regards drugs that are not seized, we have not found in the database any decision upholding a conviction where no substance at all was seized. In the abstract, the doctrine set out above does not rule this out, and SAP Málaga 2084/2026 accepts that the offence can be complete without material possession. The critical point would be to prove sufficiently the toxic nature of what was trafficked. This assessment is our own and should be checked against the specific case law before being relied on.

3. Limits and defence strategy

The defence can operate on three levels, from narrowest to broadest in scope:

1. The base facts. Each indicium must be “fully proven”. Challenging its existence, its reliability or the weight given to it is the most direct route.
2. The inference. The court must set out its reasoning. A reasonable alternative explanation, supported by counter-indicia, weakens the conclusion. STS 3191/2020, in a money laundering case, shows the counterweight: where there is direct evidence of the objective elements and constitutionally valid circumstantial evidence of participation, the defendant's failure to offer a plausible alternative explanation reinforces the rationally inferred conclusion.
3. The lawfulness of the base fact. If the indicium derives from an investigative measure that is null and void, it cannot form part of the process of inference. This is the bridge to the next part.

IV. Nullity: general framework and procedural timing

1. Three categories

Three levels should be distinguished, each with its own rules and effects:

2. Procedural route and timing

• Preliminary hearing (audiencia preliminar). Art. 785.1 LECrim (Spanish Criminal Procedure Act), as worded by Organic Law (LO) 1/2025 (in force since 3 April 2025), allows the parties to raise, before trial, the “infringement of any fundamental right”, the “nullity of proceedings” and the “nullity of the evidence proposed”. No appeal lies against the decision, but the party may lodge a formal objection (protesta) and raise the issue again in the appeal against the judgment, unless the decision brings the proceedings to an end.
• Appeals. Under art. 240.1 LOPJ, nullity as of right (nulidad de pleno derecho) and procedural defects that result in a denial of defence are to be raised through the appeals provided by law against the decision concerned. In cassation, the infringement of a constitutional provision may be relied on under art. 852 LECrim, subject to the limits the Supreme Court applies to cassation appeals against judgments delivered on appeal by the Audiencias (Provincial Courts), where only art. 849.1 is available and constitutional provisions are invoked to reinforce the alleged infringement of substantive law (STS 2032/2026).
• Incident of nullity (incidente de nulidad). Art. 241 LOPJ makes it an exceptional remedy: available only for violations of the fundamental rights referred to in art. 53.2 CE that could not have been raised earlier, and where the decision is not open to any ordinary or extraordinary appeal. The time limit is 20 days from notification or from when the defect became known, subject to an outer limit of five years. If the application is dismissed, the applicant is ordered to pay the costs.
• Timeliness. The courts require the issue to be raised in good time. SAP Málaga 4536/2025 observed that an issue raised only in the closing argument “could well have been raised at the preliminary issues stage”. On the other hand, SAP Málaga 2964/2025 acknowledges the difficulty of resolving, at the start of the trial, nullity claims that depend on an overall assessment of the evidence, and accepts that the ruling may be deferred to the judgment.

V. The main grounds for nullity

1. Telephone and electronic interceptions (art. 18.3 CE)

Legal framework. Arts. 588 bis a) to 588 bis k) and 588 ter a) et seq. LECrim. The measure requires judicial authorisation subject to the principles of speciality, suitability, exceptionality, necessity and proportionality (art. 588 bis a), by means of a reasoned order (auto) specifying, at least, the criminal act and the reasonable indications (indicios racionales), the persons under investigation, the scope of the measure, the investigating unit, its duration and its purpose (art. 588 bis c). The maximum initial duration is three months, extendable for equal periods up to eighteen months (art. 588 ter g). Extensions require an application accompanied by a report on the results obtained, and a reasoned order (arts. 588 bis e and f). Art. 588 ter a) restricts the measure to the offences listed in art. 579.1 or offences committed through computer or communication tools, and art. 588 ter i) governs the parties' access to the recordings.

Most common grounds for nullity.

• Lack of objective indicia, or fishing expeditions (prospección). STS 2273/2024 reiterates that mere suspicions, hypotheses or conjectures are not enough: the suspicions must be objectified, that is, accessible to third parties so that they can be reviewed, and supported by a factual basis from which it can be inferred that the offence has been or is about to be committed.
• Absent or insufficient reasoning in the initial order or in the extension orders.
• Breach of the principles of speciality, necessity and proportionality.
• Lack of judicial oversight of how the measure is carried out.
• Use of information from other proceedings or chance discoveries (art. 588 bis i, which refers to art. 579 bis LECrim).

Case law favouring validity. The defence must also weigh the adverse case law:

• STS 2273/2024 accepts reasoning by reference (motivación por remisión) where the police application or the report of the Ministerio Fiscal (Public Prosecutor's Office) contains all the elements needed for the proportionality assessment, even though this is not an exemplary technique.
• STS 286/2023, which draws on SSTS 797/2017, 298/2020 and 49/2021, explains that the indicia that justify the measure are not those required for a conviction or for an order committing the accused for trial (auto de procesamiento). “Good reasons” are enough, with no need for a prior “mini-investigation” or for every item of police information to be verified. If the indicia later prove to be unfounded or ambiguous, an interception that, ex ante, had to be regarded as well founded is not annulled.

Effect. SAP Málaga 4439/2013 is an example of a successful challenge in drug trafficking proceedings: it declared the first interception null and void as “unreasoned”, in breach of the secrecy of communications, and extended the unlawfulness to the extensions and, by connection, to the derivative interceptions. The judgment acquitted one of the defendants and convicted others of the offence against public health.

2. Search and entry of a home (art. 18.2 CE)

Legal framework. Art. 18.2 CE protects the home and allows entry or search only with the occupier's consent, by court order or in cases of flagrante delicto. The LECrim requires the order to be “always reasoned” and to state specifically the building or enclosed place, whether the search is to take place only by day, and the authority or official who will carry it out (art. 558). It must be served on the person concerned (art. 566) and carried out in his or her presence or that of a representative or, failing that, of an adult family member or two witnesses, and always in the presence of the court clerk (Secretario judicial, now Letrado de la Administración de Justicia), who will draw up a record (art. 569).

Grounds for nullity.

• No authorising order, or an insufficient one, or a lack of reasoning as to the indicia that justify it.
• Vitiated consent, or no valid consent from the person entitled to the home.
• Defects in execution under art. 569: absence of the required persons or of the record.
• Exceeding the authorisation as regards the place or the items covered.
• Premises of legal persons. STS 4387/2022 points out that the protection of art. 18 CE extends to the person under investigation, whether a natural or a legal person, on the terms of art. 554.4 LECrim, and that an ordinary statute, such as the Labour Inspectorate Act, cannot on its own justify an intrusion into a constitutionally protected space. That same judgment rejected the nullity claim because the entity was not a defendant and the discovery occurred in the course of an initial investigation. For its part, STC 54/2015 (a judgment of the Tribunal Constitucional, Spain's Constitutional Court) recognised a company's right to the inviolability of the home under art. 18.2 CE.
• Chance discovery and flagrante delicto. These may break the connection of unlawfulness.

Effect. According to STSJ Canarias 3077/2021, where what has been violated is the inviolability of the home, “the discovery itself, obtained from such a spurious source, cannot be assessed”.

3. Right of defence and legal assistance for detainees (arts. 17.3 and 24.2 CE)

Legal framework. Art. 520 LECrim requires the detainee to be informed in writing, immediately and in terms he or she can understand, of the facts and of his or her rights (subsection 2). These include the right to remain silent, not to incriminate oneself, to appoint a lawyer and to be assisted without undue delay, and to access those parts of the case file that are essential to challenge the detention. The appointed lawyer must attend the place of detention as quickly as possible and in any event within a maximum of three hours of being instructed (subsection 5). The assistance includes taking part in statements and identification procedures and conferring privately with the detainee, including before he or she makes a statement (subsection 6).

Grounds for nullity.

• Failure to inform the detainee of his or her rights, or information that cannot be understood.
• A statement to the police or the court taken without a lawyer, or without a prior private consultation.
• Unjustified delay in the lawyer's attendance.
• Detention without the statutory conditions that authorise it being met.

Constitutional case law. STC 103/2022 granted amparo (the constitutional remedy for the protection of fundamental rights) for violation of art. 17.1 and 3 CE, in its aspect of the detainee's right to the assistance of a lawyer during police proceedings. STC 22/2022 found a violation of the right to personal liberty (art. 17.1 and 4 CE) and annulled the orders under challenge, in a case in which one of the matters at issue was the delay in allowing the detainee to meet the appointed lawyer.

Effect. A statement obtained in breach of these safeguards cannot be assessed as incriminating evidence. Whether this extends to derivative evidence will depend on the connection-of-unlawfulness analysis.

4. Derivative evidence: connection of unlawfulness

Art. 11.1 LOPJ bars the assessment of evidence obtained “directly or indirectly” in violation of fundamental rights. STSJ Canarias 3077/2021 traces the evolution of the doctrine:

• The classic, expansive approach. Citing Supreme Court case law from 1997, it states that “the fruits of the poisonous tree must be, and are (art. 11.1 of the L.O.P.J.), legally tainted”, and that only independent evidence with no causal connection to the unlawful evidence may be assessed.
• Constitutional Court doctrine since STC 81/1998. The exclusionary effect does not follow automatically from a causal or natural connection, but from a legal connection, or connection of unlawfulness. This calls for an examination that combines an internal perspective (the nature and characteristics of the violation and the knowledge acquired through it) with an external perspective (the essential needs of protecting the right infringed). Only if the derivative evidence is legally unconnected with the violation, and protection of the right does not require it to be excluded, may it be assessed.
• Grounds for disconnection. The judgment mentions chance discovery, inevitable discovery, flagrante delicto, independent source, attenuated link and the balancing of interests.

This is the most technical stage of the defence: it is not enough to have the initial measure declared null; the defence must argue the chain of dependence through to each item of evidence it seeks to exclude, and the prosecution will try to establish a disconnection.

5. Other technological investigative measures

• Recording of direct oral communications (arts. 588 quater a to e LECrim). STC 99/2021 refused amparo in a case challenging the placing of listening devices in vehicles. The decision under appeal, which the judgment reproduces, had found that the orders specified the place, the persons and the period (the “locational, subjective and temporal specifications”) and had therefore ruled out any connection of unlawfulness with the rest of the evidence.
• Recordings made by a party to the conversation. STS 4268/2024 restates its settled case law: the recording of a conversation by one of the participants, even if made covertly, does not breach the secrecy of communications because the message has not been intercepted by a third party. In that judgment, the Supreme Court partly upheld the Public Prosecutor's appeal against a declaration of the “radical nullity” of everything done since the start of the pre-trial investigation, which the Audiencia had ordered on the basis, among other grounds, of the covert nature of those recordings. It follows that nullity requires identifying the right infringed, the measure affected and the causal link with each item of evidence.

6. Chain of custody

According to the Supreme Court, the chain of custody (cadena de custodia) belongs not to the sphere of lawfulness but to that of the reliability of the expert evidence. STS 4652/2025 of 22 October sums this up as follows:

“It is not a precondition of validity but of reliability. When the chain of custody is broken, we do not enter the field of unlawfulness or evidentiary unusability, but that of reduced reliability (impaired or even destroyed) because certain safeguards have not been respected.”

A formal irregularity (numbering, absence of a seal, delay in sending the sample to the laboratory) is not the same as a relevant break (STS 286/2023, STS 3699/2015). The party challenging it must identify the link affected, show how it bears on the identity of what was analysed and raise the matter in good time, since there is a presumption of regularity. This issue is examined in our dedicated study of the chain of custody in offences against public health.

7. Nullity of proceedings for denial of defence (art. 238.3 LOPJ)

This is the residual clause: procedural acts are null where essential rules of procedure have been disregarded and a denial of defence may have resulted. Three rules govern its scope:

• It requires an actual (material) denial of defence, not a merely formal one.
• It must be raised through the channels provided in art. 240 LOPJ, and a court hearing an appeal may not of its own motion declare a nullity that has not been sought in that appeal, except for lack of jurisdiction or competence, or violence or intimidation (art. 240.2).
• Where the final decision is not open to appeal, the only option is the exceptional incident of nullity under art. 241 LOPJ.

VI. Overview

VII. Conclusions

1. Circumstantial evidence is constitutionally valid to rebut the presumption of innocence in offences against public health, and it is the usual means of proving that drugs were intended for trafficking.
2. It requires fully proven base facts, a logical and explicitly stated inference, and the absence of reasonable alternative explanations. It does not lower the reasonable-doubt standard.
3. As regards the purpose of trafficking, the consumption thresholds (a five-day supply; 7.5 g of cocaine) are guidelines only. Trafficking may be inferred from smaller quantities where other indicia are present, and a small quantity possessed by a consumer, absent other indicia, leads to acquittal.
4. The defence must examine the lawfulness of each base fact: a telephone interception without objective indicia or without reasons, a search without a reasoned order or a statement taken without a lawyer may cause the indicium to fall away and, by connection, the derivative evidence with it.
5. Not every irregularity amounts to nullity. The case law distinguishes between unlawfulness, which bars the evidence from being assessed, and irregularity under ordinary law, such as chain of custody issues, which only affects reliability.
6. Strategy depends on timing: raising nullity at the preliminary hearing under art. 785.1 LECrim, lodging a formal objection and raising the issue again on appeal, and arguing the connection of unlawfulness item by item.

Legislation and case law cited

Legislation: Spanish Constitution, arts. 17, 18 and 24; LO 10/1995 (CP), arts. 368, 369, 369 bis and 370; LO 6/1985 (LOPJ), arts. 11, 238, 240 and 241; LECrim, arts. 520, 558, 566, 569, 579 bis, 588 bis a–k, 588 ter a, g and i, 588 quater a–e, 785, 849 and 852; LO 1/2025 of 2 January.

Decisions: STS 286/2023 of 12 January 2023 · STS 2368/2021 of 1 June 2021 · STS 3780/2019 of 12 November 2019 · STS 3191/2020 of 14 October 2020 · STS 2273/2024 of 19 April 2024 · STS 4268/2024 of 22 July 2024 · STS 4387/2022 of 11 November 2022 · STS 4652/2025 of 22 October 2025 · STS 2032/2026 of 22 April 2026 · STSJ Extremadura 1167/2026 of 22 September 2026 · STSJ Canarias 3077/2021 of 25 November 2021 · SAP Málaga 4439/2013 of 26 November 2013 · SAP Málaga 3064/2020 of 31 July 2020 · SAP Málaga 3755/2025 of 22 September 2025 · SAP Málaga 2964/2025 of 8 May 2025 · SAP Málaga 4536/2025 of 1 October 2025 · SAP Málaga 2084/2026 of 5 March 2026 · STC 54/2015 of 16 March 2015 · STC 99/2021 of 10 May 2021 · STC 22/2022 of 21 February 2022 · STC 103/2022 of 12 September 2022.

This article is for information purposes only and is no substitute for legal advice on a specific case.

Are you accused of an offence against public health on the basis of circumstantial evidence or of investigative measures that could be null and void? Contact the firm for an initial, confidential assessment of your case.

Dr. Álvaro Heredia Lara. Criminal lawyer, member no. 10.846 of the Ilustre Colegio de Abogados de Málaga (Málaga Bar Association).