Ram Singh's father has expressed doubt on the official version of events that led to his death in prison.
Mange Lal Singh said:
– Mange Lal SinghHe confessed about his mistake, then why would he commit suicide? He was prepared for any punishment the government would have given him.
Ram Singh did not commit suicide, he was murdered. He was first murdered and then his clothes were torn off to hang his corpse in his cell.
The father of Ram Singh has told the BBC that his son had a badly injured hand and could not have hanged himself.
Mangelal Singh said he had received threats from other prisoners and guards, and had been raped in prison by other inmates.
"My son has not committed suicide" he said.
The lawyer of Ram Singh has told the BBC that there was nothing to suggest he would commit suicide.
VK Anand said: "This is shocking news. There were no circumstances to suggest that he would commit suicide. He was happy with the trial, it was going smoothly."
Ram Singh was to appear before a fast track court on Monday in Saket, south Delhi, which is hearing the gang rape case.
Jail officials said that Singh, 33, was to be woken up by 5.30am to be taken to Saket Court.
The guard spotted him this morning.
All the five accused lodged in Delhi’s high-security Tihar Prison had been moved to isolated cells after being subjected to taunting and ill-treatment by other inmates of the jail.
The accused had also said they had been threatened by other convicts.
Ram Singh's lawyer, V.K. Anand, confirmed to Reuters he had committed suicide, but did not give details.
The 20-year-old brother of the victim told Reuters he was "not very thrilled with the news."
"He knew he was going to die anyway because we had and still have such a strong case against him," he said.
"Him dying on his own terms seems unfair. But, oh well, one is down. Hopefully the rest will wait for their death sentence."
A senior police official told the Associated Press news agency that a man accused in the Delhi gang rape case had committed suicide in jail.
One of the men accused in the Delhi gang rape case has committed suicide in jail, according to Indian TV station NDTV.
Ram Singh, who drove the bus involved in the attack on a 23-year-old medical student, was found dead in the early hours of Monday morning, the report said.
Singh was the main accused of five men and a juvenile who were put on trial for the attack on the 23-year-old trainee physiotherapist.
The assault triggered nationwide protests and an intense debate about rampant crime against women in India.
A 7-year-old girl is in hospital after allegedly being raped at a school in India, according to reports.
India's NDTV said around 300 protesters gathered outside the hospital in north-west Delhi where the girl was being treated.
A court in Delhi, India, is set to begin hearing evidence from witnesses in the case of the gang rape and murder of a 23-year-old physiotherapy student in December.
The five men accused have pleaded not guilty. The assault outraged India and sparked protests and debates about the treatment of women across the country.
All reporting of proceedings inside the courtroom have been banned, and lawyers are prohibited from speaking to the media.