Video from police cameras also shows a student with head injury, but Students Federation of India (SFI) activists point to his red T-shirt to say he is not Sudipto, who was wearing blue that day.
Sudipto was among the SFI students arrested on Tuesday while protesting against the Mamata Banerjee government's decision to postpone college union elections.
The Chief Minister has backed the police, which says his death was an accident caused when he hit a lamp post while hanging out of a bus taking the protesters to jail. But SFI leaders allege the police thrashed Sudipto with batons and he suffered head injuries.
One CCTV camera, located somewhere on a road leading to the jail, shows SFI activists running after a man, apparently Home Guard Biswajit Mondal. Five minutes later, at 2.47 pm, they are seen apparently roughing him up.
While the guard has filed a case of attempt to murder and criminal intimidation against SFI supporters, the police are interpreting the footage as evidence that the protesters were violent.
From another camera just outside the Presidency Jail, footage at 2.45 pm shows an injured activist being carried towards the prison. Next, he is taken towards the camera, away from the jail. He is in a red T-shirt and holds a white handkerchief to his head.
SFI activists claim the footage proves the police had baton-charged them, leaving many injured.