Police have appealed to trace three electric scooter riders who may have "vital information" about the death of another rider.
Agapita de Sousa, 34, was found with head injuries in an underpass in Bracknell, Berkshire, on 25 April.
Detectives said the riders, captured on CCTV, were potential witnesses.
A 39-year-old man from Bracknell, who was arrested on suspicion of manslaughter and theft, has been released while inquiries continue.
Detectives believe Mr de Sousa left a property at about 03:00 BST and was riding a white electric scooter with black handles.
He was injured in the Twin Bridges Roundabout underpass at about 03:30, and was taken to the Royal Berkshire Hospital where he died on 27 April, police said.
Det Ch Insp Stuart Bosley said the three electric scooter riders were caught on CCTV in Downshire Way.
He said: "I would like to stress that at this stage, we believe these individuals to be witnesses.
"It is possible that they may have seen the incident, or have some information that may prove crucial to our investigation."
Police said they believed Mr de Sousa, from Bracknell, died as a result of an "isolated incident".
Bracknell Waitrose, where he worked, previously said he was a "valued and much-loved member of our team and he will be sorely missed".