Two motorbikes were involved in a smash in Vastern Road in Reading, Berkshire at about 2.15am on Saturday, September 26.
A man on one of the motorbikes, aged 21 and from Reading, died in hospital on Friday, October 2.
His next of kin have been informed and are being supported by specially trained officers.
Meanwhile, police said on Saturday that two men have been arrested in connection with the crash, including a 20-year-old man from Oxford.
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He was taken into custody on suspicion of causing serious injury by dangerous driving, aggravated vehicle taking and theft of motor vehicle, failing to stop and failing to report an accident.
A 21-year-old man from Reading was arrested on suspicion of driving a motor vehicle when above the alcohol limit, driving whilst disqualified, causing serious injury by dangerous driving, aggravated vehicle taking and theft of motor vehicle.
Both have been released on bail.
Police sergeant Matt Cadmore, of the serious collision investigation unit, said: “Tragically, a 21-year-old man from Reading, who was involved in the collision, has now lost his life.
“His next of kin have been informed and we have specially trained officers who are supporting them at this extremely difficult time.
“I want to appeal to any drivers or pedestrians who were in the following areas: Vastern Road, Caversham Road, Napier Road, Forbury Road, Kenavon Drive, between 1am and 2.20am on Saturday (26/9).
“I would also want to extend this area to Queens Road, Kings Road and the town centre.
“If you have footage from those areas during this time or saw two motorbikes then please leave details via our website or call 101, quoting investigation reference 43260502260.”