Earlier on Wednesday, the post-mortem report of Gupta has found that there were multiple injury marks on his body.
Injuries included a fractured forehead, a broken jaw besides injuries to other parts of the body and all the injuries were sustained before Gupta died.
"We want a CBI probe. I do not want any money for his death. I want probe and I am still not sure if it will happen soon or in right direction," Sumita Sengupta, sister of the victim, told reporters.
The father of the boy said he wants justice and not any compensation.
"I am not a beggar. I do not want money. I want justice. Why was he beaten up so brutally?" asked the father, Pranab Gupta.
Besides a student strike in educational institutions in West Bengal, areas of south Kolkata is observing a shutdown. Shops kept their shutters down in areas like Garia and Tollygunge.
Gupta, a post-graduate student of Rabindra Bharati University and West Bengal state committee of the SFI died at the state-run SSKM Hospital amid charges that he was fatally injured in police action.
The SFI is the student wing of the state's opposition Communist Party of India-Marxist (CPI-M).
On Wednesday, thousands of people, including former West Bengal Chief Minister Buddhadeb Bhattacharjee, joined the funeral procession of Gupta in Kolkata.
Gupta's last rites were performed at Keoratala crematorium in south Kolkata
His body was taken to Netaji Nagar College in south Kolkata where he was the general secretary of the students' council.
Amid shouts of 'Lal Salaam', students and teachers paid floral tribute to the SFI leader.
Gupta's body was then taken to his residence at New Garia area from where he was taken to SFI headquarters in the city.
Left leaders, including Bhattacharjee, paid homage to the young leader at the SFI headquarters.
Gupta died during a police action in Kolkata at their law violation protest on Tuesday.
Reacting to Gupta's death, West Bengal Chief Minister Mamata Banerjee told reporters on Wednesday: "Every death is unfortunate..I will do everything to help his family."
Trinamool Congress (TMC) MP Derek O'Brien said some Close Circuit Television (CCTV) footages suggested that Gupta's death was an accident.
"This is a tragedy...Some of the CCTV footage suggest that this is an accident," Derek told media.
Demanding a judicial inquiry into the matter, CPI-M politburo member Sitaram Yechury told media: "The SFI student leader has died in police custody. The state government is solely responsible....A judicial inquiry is needed."
The Kolkata Police on Wednesday said a person has been arrested in connection with the matter.
The police said Gupta died after he was hit by a lamp post while alighting from the police van in which he and other protesters were being taken away after arrest.
The students had alleged that he was beaten up severely by police and pushed and even after he was taken to the SSKM Hospital he was left unattended. The students, including girls, said they were roughed up and ill-treated even inside the vehicle.
Gupta was an M.A student from Rabindra Bharati University.
The SFI was holding a protest in demand of student elections in the city's downtown area at Esplanade on Rani Rashmoni Road.
Soon there were commotion and a police action led to the clashes.
Several others were also injured in the police action and the clashes.
--IBNS (Posted on 04-04-2013)