Two police officers who followed two teenage boys on an electric bike shortly before it was involved in a fatal crash, sparking a riot in Cardiff, have been served gross misconduct notices. The Independent Office for Police Conduct (IOPC) said it was examining whether the marked van was chasing Kyrees Sullivan, 16, and Harvey Evans, 15, who were killed moments after CCTV footage caught the police vehicle just behind the bike. Family members welcomed the move by the IOPC but said they still feared they might not get justice for the boys. One member of Harvey’s family said: “If they [the officers] had not done what they did, the boys would be at home with us now. We’re happy they have been served these notices but worried that it could get blown out of the water, that there could be a cover-up. We want justice for the families.” In the hours after the riot in the Ely area of Cardiff, the South Wales police and crime commissioner, Alun Michael, claimed the riot was sparked by false rumours of a police chase. It was only after the Guardian, other media organisations and family members of the boys tracked down CCTV footage showing the police van shortly before the crash that the force admitted its officers had been following them – but insisted the van was not in the road when the boys came off the bike. The emergence of the footage led to the IOPC beginning its investigation. On Tuesday, the IOPC said it had served gross misconduct notices on the driver and passenger of the police van. It said: “Such notices advise officers their conduct is subject to investigation. They do not necessarily mean that any disciplinary proceedings will follow.” The IOPC continued: “Investigators are reviewing hundreds of video footage clips that we have gathered as a result of our house-to-house inquiries and leafleting. “We have followed up inquiries with, and taken statements from, some local residents. We have also set up witness appeal boards on relevant streets. We have reviewed initial accounts and body-worn video from relevant police officers and staff. “Our investigation continues to focus on the nature of the police interaction with the two boys prior to the collision and the appropriateness of the officers’ decisions and actions. In particular, we are examining whether at any time the decisions and actions of the officers in the police vehicle constituted a pursuit.” Michael added: “It is now important to await the outcome of the IOPC investigations and to hear their conclusions. While people would like answers now – we all would – an investigation can take time, but the IOPC has assured me that the investigation will be timely and that they will report as soon as possible.” The IOPC director, David Ford, said: “The response from the community in helping our investigators has been very positive and I am extremely grateful for this assistance. Our work will remain impartial and completely independent of the police.” Earlier this month, South Wales police said 20 people – 17 males and three females aged between 14 and 36 – had been arrested in connection with the riot. An open letter signed by more than 50 organisations and individuals including academics and campaigners and organised by the Cardiff Solidarity Group has called for an amnesty for them. It says: “The unrest seen in Ely was an understandable emotional reaction to a tragedy that may or may not have been directly caused by the actions of South Wales police.” Reacting to the IOPC’s move, the Cardiff Solidarity Group said: “We welcome the investigation into officers and hope that it is quick and effective to provide closure and a semblance of justice for the families. Heavy handed policing, and the criminalisation of young people from Ely must end.” South Wales police said the issuing of the gross misconduct notice did not “necessarily” mean that any disciplinary proceedings would follow. A spokesperson said: “The force continues to fully cooperate with the IOPC investigation.” On Saturday, South Wales police appealed for information about “hazardous driving” that took place when a convoy of bikes rode to Barry, south Wales, to pay respects to the two boys who died.