Police are investigating the incident at the Southern 100 on Thursday which left one rider dead and three more injured.
Yorkshire rider James Cowton died after the crash at the Stadium Bends section of the Billown course in the 600cc Challenge Race.
Racer Ivan Lintin is in a critical condition in hospital as a result - Michael Evans and Jamie Coward were also hurt.
The force say they are conducting the investigation on behalf of the Coroner of Inquests.
They are appealing for any information from people they haven't spoken to already, if you have any information you're being urged to contact Police Headquarters.
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