Strong suspicion under Section 173(1) StPO: the highest degree of suspicion in the investigative proceedings

Section 173(1) StPO reads as follows: "The imposition and continuation of pre-trial detention are permissible only on application by the public prosecutor and only if the accused is strongly suspected of a specific offence, has been examined by the court on the substance and on the prerequisites of pre-trial detention, and one of the grounds for detention listed in para 2 is present on the basis of specific facts." The same paragraph then contains the negative condition, pre-trial detention may not be imposed, maintained or continued where it would be disproportionate to the significance of the matter or to the expected sentence, or where its purpose can be achieved by less intrusive measures under Section 173(5) StPO.

Four cumulative prerequisites emerge from this provision, each of which must be present at the same time for pre-trial detention to be permissible at all. First, an application by the public prosecutor, since the 2008 reform of criminal procedure the prosecution has held an exclusive monopoly on this application. Second, strong suspicion regarding a specific offence. Third, the judicial examination of the accused on the substance and on the prerequisites of pre-trial detention, this examination is the mandatory hearing under Section 174 StPO, which must take place within 48 hours of admission to the prison. Fourth, the presence of a ground for detention under Section 173(2) StPO, risk of flight, risk of collusion, risk of repeated offending or risk of execution.

These are joined by two negative prerequisites that are just as decisive in practice. The proportionality clause prohibits pre-trial detention where it would be disproportionate to the significance of the matter or to the expected sentence. The subsidiarity clause prohibits it where its purpose can be achieved by less intrusive measures. Anyone framing the defence around Section 173(1) StPO checks these six points one by one, each, taken individually, can lead to release if it is not met.

A common misconception from the perspective of clients: the assumption that an arrest itself "proves" strong suspicion. In fact, the arrest under Section 170 StPO is only the police pre-stage, permissible under lower requirements; strong suspicion is examined for the first time by the detention judge at the mandatory hearing. The mere fact that someone has been arrested says nothing about whether the court will ultimately confirm that this threshold has been crossed. The thresholds are not the same: Section 170(1) StPO permits arrest already at the level of simple or reasoned suspicion, while Section 173(1) StPO requires the additional, higher level of strong suspicion for pre-trial detention (Kier, marginal no. 9.20). Overlooking this gradation means overlooking one of the most effective levers of early defence work.

The Austrian Code of Criminal Procedure recognises three levels of suspicion. Each level permits successively deeper interventions in the rights of the accused, and each is tied to specific evidence and standards of proof. Anyone who wants to place the level of suspicion correctly has to know which level the prosecution is claiming in the specific case and whether the evidence supports that level.

First level: initial suspicion (Section 1(3) StPO). Initial suspicion exists where, on the basis of specific indicators, it can be assumed that a criminal offence has been committed. This threshold is low, a credible complaint, an initial witness observation or a seized data carrier will generally be enough. Initial suspicion is sufficient to formally conduct an investigation, to examine the accused and to request files. Interventions affecting fundamental rights are only permissible to a limited extent at this stage.

Second level: reasoned or simple suspicion. This middle level is required in various provisions of the StPO without being expressly defined by statute. It calls for "specific facts" that support a suspicion in a way that justifies a concrete intervention. Practically central examples include Section 116 StPO (seizure), Section 119 StPO (house search) and Section 121 StPO (seizure of data on residential premises). Reasoned suspicion must be supported by concrete pieces of evidence, statements, traces, data; the mere gut feeling of the investigators is not enough.

Third level: strong suspicion (Section 173(1) StPO). The highest degree of suspicion in the investigative proceedings. It requires that, on the basis of the file, there is a high probability that the accused has committed the offence in question. This probability must be supported by specific facts, and the elements pointing towards perpetration must outweigh the elements pointing against it. The mere possibility of perpetration is not enough, nor is the abstract assumption of a connection with the offence. On the other hand, detention proceedings do not require "overwhelming evidence" of the kind that would be needed for a conviction, the level of suspicion remains below the full evidentiary threshold of the main trial.

This gradation is more than theoretical hair-splitting. It steers the defence strategy: if the prosecution is already asserting strong suspicion at the moment of arrest, the defence must show that the evidence does not support that level, for example because a central piece of evidence is ambiguous, a witness statement contains credibility gaps, or an alleged factual link is relativised by exculpatory evidence. If the level of suspicion drops to the second tier in the court's assessment, pre-trial detention becomes inadmissible, even where a ground for detention would be present.

Indicators standard. Strong suspicion may also be based on circumstantial evidence alone. The Supreme Court (OGH 11 Os 17/93) requires for this "the existence of indicators which, although not each of them on its own, in their interconnection provide a logically and empirically sound and tenable basis for the assumption of perpetration" (cited by Kier, marginal no. 9.17). From a defence perspective this yields a clear examination structure: each individual indicator is assessed for evidentiary weight, ambiguity and alternative explanation, and the interconnection must hold, not merely the sum of individual elements. Equally decisive is the weighing: the incriminating factors must outweigh the exculpatory circumstances, otherwise suspicion is not strong.

Weighing decision in the individual case. The finding of strong suspicion is, according to Kier (marginal no. 9.18), a weighing decision that is tied exclusively to the concrete individual case. Schematic tables, abstract evidentiary-weight charts or "in comparable cases the result was such-and-such" arguments do not carry. This opens a back door for the defence: any change in the evidentiary picture forces the court to undertake a new weighing, a schematic adoption of earlier reasoning is impermissible and can be challenged on appeal.

Presumption of innocence, cleanly delineated. A line runs here that often remains blurred in detention defence. For the weighing decision on strong suspicion itself, the presumption of innocence under Article 6(2) ECHR applies without restriction, the incriminating circumstances must outweigh the exculpatory ones. For the "specific facts" on which the ground for detention under Section 173(2) StPO is based, however, it does not apply (OGH 13 Os 125/06s; Kier, marginal no. 9.45). Appeals based solely on the claim that the court violated the presumption of innocence when finding risk of flight, risk of collusion or risk of repeated offending have no prospect of success. Counsel who keep both lines cleanly separated formulate effective appeal grounds.

Special case: after a first-instance conviction. Where a panel court (Schöffengericht or Geschworenengericht) has issued a guilty verdict, the courts regularly derive strong suspicion from that verdict and do not independently scrutinise it any further (Kier, marginal no. 9.19). This is standard practice, not an automatic rule: if the guilty verdict carrying the detention is set aside on appeal, suspicion can no longer be based on it, the court must re-examine the file. At this stage the detention review or appeal brief must be tailored to the precise scope of the setting-aside.

Confirming strong suspicion in the investigation phase is exclusively a matter for the court, specifically for the detention and legal protection judge (Haft- und Rechtsschutzrichter, abbreviated HR-Richter) at the competent Regional Court (Landesgericht). Section 33(1) no. 1 StPO assigns the HR-Richter competence over applications by the public prosecutor for the imposition, continuation or lifting of pre-trial detention during the investigation. The police and the public prosecutor can assert strong suspicion, only the court can confirm it.

The procedure follows a clearly regulated pattern. After the arrest the accused is admitted to the prison. Section 174(1) StPO requires that the arrested accused be examined by the court on the prerequisites of pre-trial detention without delay after admission. At this mandatory hearing the HR-Richter hears the accused in person and gives the prosecution, the accused and defence counsel an opportunity to comment. The court must then decide, within 48 hours of admission to the prison, whether the accused is to be released or pre-trial detention is to be imposed; less intrusive measures are to be applied where appropriate.

In the reasoning of the detention order the HR-Richter must disclose the specific facts on which the strong suspicion is based. Section 174(3) StPO governs the duty to give reasons, alleged offence, grounds for suspicion, ground for detention, period of validity, instructions on remedies. A generic or formulaic reasoning is impermissible; it can be successfully challenged on appeal to the Higher Regional Court, which reviews whether the reasoning of the suspicion holds up.

Competence shifts once an indictment has been filed. If pre-trial detention is maintained or newly imposed during the main trial, the trial court decides, typically a single judge, a lay-assessor court or a jury court depending on the prescribed sentence. Appeals against detention orders are heard by the Higher Regional Court (Sections 87 and 88 StPO). Where there is an evident violation of fundamental rights, a separate fundamental-rights appeal to the Supreme Court (OGH) is also available.

Strong suspicion is not a value fixed once and for all. Section 175(1) StPO expressly provides that pre-trial detention is to be lifted immediately as soon as the prerequisites for its imposition fall away, and this includes the suspicion. Anyone who has the level of suspicion reassessed after an arrest or an initial detention hearing can secure release even at an advanced stage of the proceedings.

Typical configurations in which strong suspicion falls away. First: new exculpatory evidence comes to light, an alibi witness comes forward, a technical piece of evidence (DNA analysis, location data from the mobile network, video footage) refutes the incrimination, or a previously incriminating witness credibly retracts. Second: the sole source of incrimination loses evidentiary weight, for example because the central statement becomes self-contradictory or the credibility of the incriminating witness is undermined by newly known circumstances. Third: the legal classification of the alleged offence shifts, if, on the basis of the file, what was initially treated as a felony shrinks to a misdemeanour, strong suspicion may still exist with regard to the misdemeanour, but proportionality may now tip against detention.

Legal consequences of the suspicion falling away. If the level of suspicion drops below the threshold of strong suspicion, pre-trial detention must be lifted, that is not a matter of discretion. The lifting is ordered by the court that imposed the detention, on application or of its own motion. On appeal the Higher Regional Court can lift the detention directly if it concludes that strong suspicion is not, or is no longer, present. The detention periods under Section 175 StPO continue to run until the detention is lifted, so every day without a sustainable level of suspicion amounts to an unlawful deprivation of liberty.

In practice the loss of strong suspicion is an important lever for the defence in each detention review hearing after 14 days, 1 month and 2 months. The court re-examines the level of suspicion every time; any change in the file, newly received expert reports, further witness statements, fully evaluated data carriers, can lower the level of suspicion. Defence counsel who consistently exercise access to the file under Section 51 StPO and systematically document the shifting evidentiary position will have the strongest argument at the next detention review hearing.

A recurring source of error in detention defence is the conflation of suspicion and ground for detention. Section 173(1) StPO requires both, cumulatively. Strong suspicion alone is not enough; a ground for detention alone is not enough. Defence counsel who only attack the ground for detention (for example by neutralising the risk of flight through a fixed residence and the surrender of the passport) without addressing the suspicion leave an important lever unused. Conversely: counsel who only attack the suspicion but let the ground for detention stand unchallenged may achieve nothing if the court confirms the suspicion.

Step 1: access to the file under Section 51 StPO. Before any detention hearing, including before the mandatory hearing, counsel must know the full evidentiary record. Section 51 StPO grants in principle unrestricted access to the file; in the detention and legal protection phase access is in practice almost always open, because grounds for confidentiality rarely prevail at this stage. The first step of the defence is therefore a request for a complete copy of the file, if possible before the mandatory hearing. Economically important: up to the first detention review hearing, defence counsel are entitled under Section 52(2) no. 2 StPO to a free copy of the file, which makes the quick instruction of counsel financially predictable. Substantively decisive: for the assessment of suspicion, aspects of access to the file may not be excluded by the court (Section 51(2) last sentence StPO), only the complete content of the file allows the assessment whether the incriminating facts outweigh the exculpatory ones (Kier, practice tip marginal no. 9.20).

Step 2: dissect the chain of incriminating evidence. Strong suspicion stands or falls with the chain of incriminating evidence. Practically this means: each piece of incriminating evidence is examined individually for evidentiary weight, plausibility of the statement, chain of traces, evaluability of technical data, conditions under which incriminating witnesses observed, possible motives for incriminating statements. Where incrimination hangs on a single statement, the threshold of suspicion is particularly fragile.

Step 3: prepare less intrusive measures in writing. Even if the suspicion is confirmed, the subsidiarity clause tips pre-trial detention as soon as less intrusive measures are sufficient. Counsel should therefore present a concrete package already at the mandatory hearing, fixed residence, surrender of travel documents, reporting duty (several times a week or daily, depending on the risk of flight), contact bans for co-suspects or witnesses, and where appropriate provisional probation supervision and treatment requirements. The individual measures are set out in detail on the topic page on less intrusive measures.

Step 4: safeguard the appeal period. Even if the HR-Richter affirms strong suspicion at the mandatory hearing and imposes pre-trial detention, an appeal under Sections 87 and 88 StPO to the Higher Regional Court must be considered as a matter of course. The period is 14 days from service of the written copy of the detention order, which must take place within 24 hours of pronouncement (Section 88(1) StPO; Kier, marginal no. 9.61); for subsequent orders on the continuation of pre-trial detention, the shorter period of 3 days from pronouncement applies under Section 176(5) StPO. The Higher Regional Court may reach the opposite conclusion, particularly where the reasoning of the HR-Richter shows gaps or where newly available exculpatory evidence must be taken into account. More on this on the topic page on detention appeals.