The postmortem report is believed to have claimed that the 22-year-old had suffered two severe head injuries and a blow to the jaw.
Gupta, an activist of Student Federation of India (SFI), student wing of the CPI(M), allegedly have been killed due to police brutality during a protest rally against the Chief Minister on Tuesday, April 2.
Overruling such allegations and postmortem report, the Trinamool Congress chief reiterated, "It is an accident. It is very unfortunate. It is not police assault."
However, eye-witnesses said that Sudipto died as police had badly beaten him up and threw him out of the bus, where he and his fellow SFI protesters were bundled into after they protested against Mamata's decision of not allowing elections in colleges on Tuesday.
SFI General Secretary Satarup Ghosh, an eyewitness himself, said, "He was hit on his head so hard that one of his eyes came out."
"We were courting arrest when the policemen started beating us in the bus. One of the policemen hit Sudipto's head with a lathi and he fell down. When we demanded immediate medical help for him, the police refused," Ghosh said.
"There was a scuffle inside the bus as the students shouted slogans. One of the students hit a lamp post and was critically injured," Javed Shamim, Joint Commissioner of Police, Law and Order, said.
Another protest march in connection with Sudipto's death was held in Kolkata. The CPI(M) workers and leaders blocked several roads in the city protesting against Mamata's government.