The row was triggered with police claiming that the death of Sudipto Gupta was an accident, while the opposition Left Front alleged he succumbed to injuries sustained during a heavy lathi-charge by police.
West Bengal Chief Minister and Trinamool Congress supremo Mamata Banerjee was on the defensive as she called the Tuesday death of Gupta "unfortunate" and pledged to help his distraught family.
The Left Front, however, lambasted Banerjee for commenting on the death of the activist in police custody before a probe had been conducted. It also alleged that she was trying to establish the death as an "accident".
The chief minister visited the state-run hospital Wednesday afternoon where Gupta succumbed to his injuries. She said many activists of her party had been killed when they crashed into lamp posts while travelling by trains.
State Left Front chairman and CPI-M state secretary Biman Bose said Banerjee's comment on the SFI leader's death before any inquiry was "wrong".
"The chief minister has made some comments. She is not only a chief minister but also holds the home portfolio. If she comments on the death, then is there any scope of an inquiry," Bose told a media conference here.
The SFI is the student wing of the Communist Party of India-Marxist (CPI-M).
Gupta, 24, a post-graduate student of Rabindra Bharati University and an SFI activist, died allegedly after policemen assaulted him in custody.
Left activists said Gupta was "mercilessly beaten" while he and other students who had staged a protest seeking elections in colleges were being taken in a bus to the Presidency Correctional Home.
In the process, Gupta reportedly fell from the bus and collapsed after crashing against a lamp post, said an SFI member.
"He was hit on his head so hard that one of his eyes popped out," added West Bengal SFI joint secretary Shatarup Ghosh.
Police, however, said that the activist died after he crashed into a lamp post while being taken to jail.
The West Bengal Human Rights Commission ordered a probe into his death, for which celebrated filmmaker Mrinal Sen blamed Banerjee.
"Who is responsible? The one who rules the state, under whom the police are, that is the chief minister is responsible for this death," Sen said.
Gupta's body, wrapped in the CPI-M's red flag, was taken in a flower-bedecked hearse from the hospital to the Netaji Nagar College where he was general secretary of the students' council.
Grieving students and teachers offered floral tributes amid cries of "Lal Salam!"
The body was then taken to Gupta's residence where his father broke down.
The inconsolable 63-year-old Pranab Gupta, a widower, said his son "used to dream of a new social order, a new dawn".
He said he would not let the death go in vain and fight for justice.
Helped by CPI-M and SFI leaders, the grieving father wobbled towards the vehicle, folded his hands, and then placed flowers on the body.
The body of the deceased activist was then taken to the SFI state committee office, where senior Left Front leaders, including Biman Bose, former chief minister Buddhadeb Bhattacharya and leader of opposition in the state Assembly Suryakanta Mishra, garlanded the body.
CPI state secretary Manju Kumar Majumdar and Forward block state committee secretary Ashok Ghosh also paid their last respect to Gupta. Renowned filmmaker Tarun Majumdar was present at the SFI office.
The funeral procession, in which thousands of people from different walks of life participated, traversed various arterial roads and finally reached at Keoratala crematorium at south Kolkata, where the body of the SFI activist was consigned to flames.
Gupta's elder sister Sumita Sengupta, however, took a dig at the CPI-M, alleging that the deceased activist had been brainwashed by the party.
"CPI-M brainwashed my brother. The leaders used him for the party's interest," Sengupta said.
Meanwhile, Taking suo motu cognizance of the death, the West Bengal Human Rights Commission ordered the Kolkata police commissioner to submit a report in seven days.
The commission has also formed its own investigating team and will examine witnesses and other evidence cause of Gupta's death.
Even the Congress voiced dismay.
"With (Trinamool) taking over, we had thought the state will witness change. What I see is the politics of police killing students ... has come back," state Congress president Pradip Bhattacharya said.
The death in Kolkata triggered protest demonstrations in Chennai, Kerala and New Delhi.
In the national capital, over 100 students of the Jawaharlal Nehru University staged a noisy protest outside Banga Bhawan, which belongs to the West Bengal government.
Some students tried to scale the boundary wall but were stopped by police.
The Left Front announced that it would hold demonstrations across the state Thursday to protest against the shocking death.
"The Left Front will carry out agitations in all the districts tomorrow," Bose told reporters.
The CPI-M has also called for a 12-hour strike in south Kolkata's Garia-Tollygunge-Dhakuria areas Thursday.