32 BOUYID v. BELGIUM JUDGMENT persons responsible will risk falling foul of the required standard of effectiveness. 121. A requirement of promptness and reasonable expedition is implicit in this context. While there may be obstacles or difficulties which prevent progress in an investigation in a particular situation, a prompt response by the authorities in investigating allegations of ill-treatment may generally be regarded as essential in maintaining public confidence in their adherence to the rule of law and in preventing any appearance of collusion in or tolerance of unlawful acts. 122. The victim should be able to participate effectively in the investigation. 123. Lastly, the investigation must be thorough, which means that the authorities must always make a serious attempt to find out what happened and should not rely on hasty or ill-founded conclusions to close their investigation. (b) Application to the present case 124. The Court considers that the applicants’ allegations – as set out in the complaints lodged with the domestic authorities – that they were subjected to treatment breaching Article 3 of the Convention by officers at the Saint-Josse-ten-Noode police station were arguable. Article 3 thus required the authorities to conduct an effective investigation. 125. The Government submitted that the manner in which the investigation was conducted was satisfactory in the light of the criteria established in the case-law, as set out above. 126. The Court does not share the Government’s view. 127. It notes that after the applicants had lodged a civil-party complaint, an investigation was initiated and the two police officers implicated by the applicants were charged with using violence against individuals in the course of their duties and, in particular, with intentional wounding or assault, and with engaging in arbitrary acts in breach of the rights and freedoms guaranteed by the Constitution. The investigation was conducted in accordance with statutory requirements, under the authority of an investigating judge. It was therefore under the control of an independent authority. Furthermore, there is nothing to suggest that the applicants were unable to participate in it. 128. Nevertheless, the investigating judge, who would appear not to have ordered any specific investigative measures in person, confined himself to asking the investigation department of Committee P to take note of the applicants’ civil-party application, to interview them in order to ascertain the details of their complaint, to draft a report on the conduct of the Bouyid family, to draw up a list of the cases brought against them and complaints filed by them and to explain what action had been taken in that connection. He failed to hold, or arrange for, a face-to-face confrontation