Police said a man on trial for the gang rape and fatal beating of a woman aboard a New Delhi bus committed suicide in an Indian jail, but his lawyer and family allege he was killed.
Ram Singh, who was accused of driving the bus on which the 23-year-old student was raped by a group of six men in December, was under suicide watch at New Delhi's Tihar Jail when he hanged himself with his own clothes police officials said.
His death is raising further questions about a criminal justice system already being criticised for failing to protect the nation's women.
Singh and his four fellow defendants were facing the death penalty if convicted of the attack, which horrified Indians and set off national protests.
A sixth accused is being tried and jailed separately because he is a juvenile.
Ram Singh's family and lawyer alleged foul play in his death.
Ram Singh's father, Mangelal Singh, said his son had been raped in prison by other inmates and had been repeatedly threatened by inmates and guards.
Nevertheless, he said he visited his son four days ago and the man appeared fine and gave no hint of the despair that could drive him to take his own life.
Ram Singh, 34, also had a badly injured hand and would have been unable to orchestrate a suicide, his father said, speaking from outside his small home in a New Delhi shanty town.
"It was not suicide," he said, insisting he would push for a top level investigation into the death.
Mangelal Singh said he feared for the safety of another son who is also on trial in the rape case.
Meanwhile, Shiela Dikshit, Chief Minister of Delhi said a post mortem examination will be conducted to investigate the cause of his death.
Lawyers for the defendants had previously accused police of beating confessions out of the men.
"The prosecution is saying that this is suicide. This is not suicide, this is murder, a planned murder," said Ajay Prakash Singh, one of the defence lawyers.
The defendants were being housed in separate buildings on the jail grounds and were all under suicide watch, a jail official said on condition of anonymity because he was not authorised to speak publicly on the matter.
Indian jails have a reputation for overcrowding, poor management and brutal treatment of inmates.
Tihar Jail is badly overcrowded with nearly twice as many prisoners as it was designed to hold.
The rape victim and a male friend were attacked after boarding the bus December 16 as they tried to return home after watching a movie, police say.
The six men, the only occupants of the private bus, beat the man with a metal bar, raped the woman and used the bar to inflict massive internal injuries to her, police say.
The victims were dumped naked on the roadside, and the woman died from her injuries two weeks later in a Singapore hospital.