5.  The applicants were born in 1969, 1968 and 1972 respectively and live in Lanžhot (Messrs. Bátěk and Elsner) and Břeclav (Mr Blažej). 6.  From September 2003 to January 2004 the applicants were employed by the Lanžhot Customs Office on the border with the Slovak Republic. On 1 December 2003, pursuant to Article 158e of the Code of Criminal Procedure (“the CCP”) an undercover police agent infiltrated the team of customs officers. As a result of her observations over the following two months, the customs officers were suspected of corruption, namely taking bribes from truck drivers in exchange for granting priority or trouble-free customs clearance. The undercover agent left the Customs Office on 6 February 2004. 7.  During March and April 2004 testimony was taken in the presence of a judge from twenty truck drivers from different countries in accordance with the provisions of Article 158a of the CCP, that is to say this step was taken as an urgent or non-repeatable measure (neodkladný nebo neopakovatelný úkon). The records show that the drivers’ testimonies were similar. According to the applicants, interviews with four of the drivers were of decisive significance. Three of them were of Romanian nationality and one of them was a Bulgarian citizen. The applicants, being not yet charged, were not present at these interviews. 8.  Witness I.P.D. testified that it was common practice for the customs officers to ask drivers for documents and to check whether there was some money enclosed. If not, the drivers had to wait for hours to be cleared. He admitted that he had paid bribes on two or three occasions but he could not remember individual customs officers.
Witness C.D. testified that he had always had to pay 5 euros (EUR) in order to avoid inconvenience during customs clearance. He described one customs officer as a corpulent person with thinning brown hair. He did not remember any other officer.
Witness S.B. testified that he had paid 5 EUR on each of the ten trips he had made to pass the customs control. He was not able to describe any of the customs officers.
Witness A.A.U. confirmed the existence of corrupt practices at the customs office in question but could not specify any particular person. 9.  On 22 April 2004 the applicants were charged, together with fifteen other individuals, with abuse of the authority of public official and accepting bribes. In February 2005 they were officially indicted. 10.  On 14 December 2005 the Břeclav District Court (okresní soud) heard the police agent as an anonymous witness (utajený svědek) under the provisions of Article 55 § 2 and Article 209 of the CCP. She gave her testimony outside the courtroom using an audio streaming device. She did not recount any specific case of the acceptance of a bribe, stating only that her reports and the information therein were fully reliable. The third applicant was present at the hearing. He was represented by a defence counsel. The other two applicants were absent and were represented by a substitute defence counsel. Only the third applicant put a question to the anonymous witness.
In the course of the trial, the applicants argued that the agent would have been unable to see any other customs officers from her work-station, that none of the alleged acts had been filmed by the cameras installed at their workplace, and that the officers’ numbered rubber stamps could have been used by other people. 11.  On 25 May 2006 the District Court found the applicants and other accused persons guilty as charged. They were sentenced to one year’s imprisonment suspended for two years’ probation and were fined. The court established the factual background to the body of evidence. The agent’s written report constituted directly incriminating evidence. The court further relied on customs documents stamped using the personal rubber stamps of specific customs officers, comparing these with the testimony of the truck drivers, the records of service rotations and the database linking the applicants to the times at which the interviewed truck drivers obtained their customs clearance. The District Court stated:
“As regards the defendant Roman Bátěk, he is incriminated by the relevant documentary evidence referring to counts 2 and 3 of the indictment and counts 4 and 5 of the indictment, from which it is apparent that he used a rubber stamp with the number 005 and that his personal number was 20627, these numbers appearing on the relevant documents. When it comes to counts 2 and 3 of the indictment, he is also incriminated by the witness statements of the Bulgarian driver [D.] and the Romanian driver [C.D.] who, according to their records, passed the border crossing point at the time in question, and their papers and travel documents bear the respective numbers of the defendant Bátěk. The above fully corresponds to the report from the defendant’s employer regarding the placement of the defendant, i.e. where ‒ that is to say at which work-station ‒ he was positioned at the time concerned. As to counts 4 and 5 of the indictment, the defendant Bátěk is also incriminated by a police officer of the Czech Republic who saw the defendant accepting a bribe and recorded this fact in the corresponding document, produced in evidence, which also corresponds with the testimony of the undercover agent given before the court.
As regards the defendant Radek Blažej, he is incriminated by the documentary evidence produced as regards counts 6 and 7 of the indictment, specifically the control sheets showing his personal number 16898 and rubber stamp number 090. He is also incriminated by the testimony of the Romanian driver [C.D.] and by a report from his former employer stating the defendant’s whereabouts at the time concerned. As to count 7 of the indictment, the defendant Radek Blažej is also incriminated by the undercover police agent of the Czech Republic who saw the defendant accepting a bribe.
As regards the defendant Karel Elsner, he is incriminated on counts 8, 9 and 10 of the indictment by the documentary evidence produced, especially by control sheets which were stamped with his personal number and also by other use made of his personal number, as is apparent in the corresponding computer records. He is also incriminated by the witness statement of [S.D.], who submitted details of his border crossing to the authorities and notes of bribes given at a specific time and place. As to count 9 of the indictment in relation to the defendant Karel Elsner, the witness stated that on 10 November 2003 he gave a bribe at a particular time and ‒ by checking the driver and the documentation relating to his border crossing ‒ it was established who had cleared him and who had stamped his documents, from which it is clearly apparent that it was the defendant Elsner who carried out the administrative measures concerned and hence received the bribe. As to count 10 of the indictment, Karel Elsner is also mentioned in the anonymous agent’s report.” 12.  The District Court explained that the truck drivers’ statements were read out at the hearing pursuant to Article 211 § 2 b) of the CCP. The drivers had been interviewed in the presence of a judge during the pre-trial stage of the proceedings, because it had been deemed necessary to take the step of obtaining their testimonies as an urgent or non-repeatable measure since they were foreign nationals and it would have been almost impossible for the court to reach them at a later stage. The undercover police agent was heard as an anonymous witness pursuant to Article 209 of the CCP because of her potential future activities. 13.  The applicants appealed against the judgment. They firstly argued that the truck drivers could have been questioned under the corresponding international treaties ‒ namely the European Convention on Mutual Assistance in Criminal Matters and bilateral treaties on mutual judicial assistance with Romania (treaty of 25 October 1958) and Bulgaria (treaty of 25 November 1976) ‒ and that they could have been granted immunity in exchange for testifying. They also contested the legal grounds and the necessity for the non-disclosure of the identity of the undercover police agent. According to them, she did not risk bodily harm or any other danger of interference with her fundamental rights as required by Article 55 § 2 of the CCP. The argument about her future activities was not sufficient justification. Moreover, the delays between the questions asked at trial and her replies implied that she had had with her some notes or someone whom she had consulted about her answers before replying. 14.  On 22 March 2007 the Brno Regional Court (krajský soud) rejected the applicants’ appeal as unsubstantiated, arguing as follows:
“(...) the hearing of an undercover police agent as a witness is in practice exceptional, occurring only in the particular circumstances of a specific case and in the interests of proper clarification and vindication of particularly serious criminal actions and the conviction of the perpetrators thereof. In such circumstances, and when such an agent is heard as a witness, Article 55 § 2, Article 183a § 4, and Article 209 of the CCP would be applicable. In the instant case, the provisions of the CCP regulating the agent’s testimony were not violated and the allegations of some of the defendants that the agent had been heard as an anonymous witness in order to allow her to consult her notes or another person are unsubstantiated. The first-instance court had no doubts about the agent’s reliability as a witness. She reliably described how she had obtained the information about the criminal activity of the accused and how she had evaluated, recorded and processed it (...)
Under Article 160 § 4 of the CCP, a non-repeatable measure is a measure which cannot be repeated before the trial court. Questioning a witness who is a foreign national or stateless person without a permanent residence permit in the Czech Republic can be considered to be this kind of measure. None of the witnesses had a link to the Czech Republic of the kind which could have justified the conclusion that they would remain in the country or appear if summoned. The witnesses merely pass through the territory in the course of their work as truck drivers. The interviews with these witnesses were conducted in accordance with the provisions of the Code of Criminal Procedure. The allegations of the defendants that the witnesses did not even know the content of the records they had signed, and that they had been forced to testify and promised immunity if they stated particular facts, are not substantiated by the case file, and no other facts corroborating these allegations have been ascertained. It is apparent from the file that the truck drivers were questioned in the presence of an interpreter and in the presence of judges of the Břeclav District Court (...). Under Article 158a of the CCP, a judge who performs the urgent or non‑repeatable measure of examining a witness or in an identity parade also bears responsibility for the legality thereof." 15.  The applicants filed a constitutional appeal alleging a violation of Article 6 §§ 1 and 3 d) of the Convention and complaining about the depositions of the truck drivers and the anonymous witness. 16.  On 2 April 2009 the Constitutional Court (Ústavní soud) dismissed the constitutional appeal as manifestly ill-founded. It stated that the complaints raised at the previous instances had been properly addressed and that the courts had provided sufficient justification to show that the evidence had been obtained in accordance with the provisions of the CCP.