Kyrees Sullivan, 16, and Harvey Evans, 15, died in the crash after they were followed by the police.
A police officer driving a van who followed two teenagers before they both died in an e-bike crash is being investigated for dangerous driving.
Kyrees Sullivan, 16, and Harvey Evans, 15, died after the bike they were riding crashed in Ely, Cardiff, in May.
The driver of the police van, along with another officer in the vehicle, had previously been served with gross misconduct notices.
The deaths led to riots which saw 15 officers injured and dozens arrested.
South Wales Police said it “continues to fully co-operate” with the Independent Office for Police Conduct (IOPC)’s investigation.
The IOPC has confirmed that the driver of the police van will now face a criminal investigation.
The police watchdog said that the serving of notices and the criminal letter do not necessarily mean that disciplinary or criminal proceedings will follow.
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The IOPC added that a “key consideration” of the investigation, which began three months ago, is to establish if the officers’ decisions and actions in the police van constituted a pursuit.
It added that investigators are examining hundreds of video clips and have obtained a number of statements from local residents.
“I would like to emphasise again that we remain committed to establishing the facts of what happened,” said IOPC head David Ford.
“We will continue to provide regular updates to the families of Kyrees and Harvey, to make them aware of developments in the investigation.”
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“Our thoughts and sympathies remain with the family and friends of Kyrees and Harvey and everyone impacted by the tragic loss of two young lives in Ely,” added Mr Ford.
“Our independent investigation is progressing well and I want to again thank the local community for the support provided to our investigation, including through the sharing of CCTV evidence.
“We would still encourage anyone who believes they have useful information to come forward to us.”
Following the deaths, rumours rapidly spread on social media that the boys had been chased by police before the crash.
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Cars were set alight and fireworks thrown at police after 100 to 150 people gathered in Ely on 22 May, the evening of the crash.
A total of 27 people have been arrested following the disorder.
Paying tribute to Harvey days after the crash, his mum said: “He lived life to the full, he had a big heart and deep down he truly cared”.
Kyrees’s family described him as “a loving, caring handsome young man”.
Image source, PA Media
Thousands of people lined the street of Ely at their joint funeral in July.
The procession included four hearses and nine Rolls-Royces, and was led by a group of motorcycles.
Following the service the boys, described as best friends by their families, were buried in the same plot.
A spokesperson for South Wales Police said: “The force continues to fully co-operate with the IOPC investigation and is providing them with information and material, including CCTV footage and body-worn video.
“We acknowledge the impact Kyrees Sullivan’s and Harvey Evans’s deaths have had on their families, friends, and the wider community. Our thoughts and condolences continue to be with them.”