Police are investigating footage from a CCTV camera in Ely which appears to show two young people on an electric bike being followed by a police van just moments before a crash that killed two teens.
Police said they were called to reports of a crash in Snowden Road at 6pm on Monday night (May 22), and the video from a house in the area appears to show a bike being followed by police at 5.59pm.
South Wales Police has said previously that the collision had "already occurred" when officers arrived.