The main accused in the fatal gang-rape of a student on a bus in New Delhi last December was found dead in his prison cell Monday, prompting fury from the victim's family and accusations of murder.
Officials at the maximum-security Tihar Prison in the Indian capital said bus driver Ram Singh, 34, had hanged himself with a makeshift noose.
But Singh's parents said there was no way their son could have committed suicide and he had told them his life was in danger, while his lawyer said the death should be treated as murder.
Singh, one of six people on trial over the attack which brought simmering anger about sex crime in India to the boil, was found dead at around 5:15am.
"He tied all his clothes together and used the ceiling grille and a wooden stool to hang himself," the prison's law officer Sunil Gupta told AFP.
Gupta said a magistrate would investigate any security lapses surrounding the death.
The father of the 23-year-old gang-rape victim told AFP it was clear authorities had been negligent.
"We don't understand how could the police fail to protect Ram Singh. They knew he was the prime accused," said the father, who cannot be named for legal reasons.
"How could they let him choose the way he wanted to die?"
Singh was making regular appearances in a New Delhi court where he faced murder, rape and kidnapping charges over a crime that ignited street protests and soul-searching about India's treatment of women.
Four other men charged over the gang-rape face the death sentence if convicted in a special fast-track court, the proceedings of which are subject to a media gagging order. They have all pleaded not guilty.
A sixth 17-year-old suspect is being tried in a juvenile court where he faces a maximum three years imprisonment.
Lawyers have previously claimed the defendants had been attacked and Ram Singh's attorney V.K. Anand said police should open a murder inquiry.
"If he had committed suicide then he would have left a suicide note," he told AFP.
Ram Singh's father, Mange Lal Singh, said his son would have struggled to rig up a ligature as a result of a hand injury he sustained in a road accident several years ago.
"He couldn't have committed suicide with just one hand," he said.
His son had been sharing his cell with two other men, he added, contradicting claims from jail authorities that he was in solitary confinement.
Despite Ram Singh's not guilty plea, his father indicated he acknowledged his guilt.
"My son told me that he was ashamed by what had happened on 16 December. He said that he would accept whatever punishment is given to him," he said.
He also said his son hat told him his life was in danger and that he had been sodomised by other inmates.
The bus victim, who was studying physiotherapy, died on December 29 at a hospital in Singapore.
As well as being repeatedly raped, she was also violated with a metal bar, leaving her with massive internal injuries.
Singh, a widower whose younger brother Mukesh is also an accused, was the regular driver of the private bus, normally used to ferry school children.
He was the first to be arrested after the attack, when the police pulled over the vehicle the next day. Detectives immediately became suspicious because the seats of the bus were freshly cleaned.
"He pretended as if it was just another normal day and he was back to work," Chhaya Sharma, a deputy commissioner of police who was in charge of the gang-rape investigation, told AFP in a recent interview.
"We asked him why had he been washing the bus on a chilly winter morning when he knew that he had to take children to school. He said: 'Well, it is good to have a clean bus.'"
Police say Singh and friends had enjoyed a meal together and had been drinking before deciding to take the bus out for a night-time joy ride, luring passengers who believed it was genuine public transport.
A 28-year-old software specialist who had spent the night at the cinema with the student victim was also severely beaten with the metal rod.
A senior police officer investigating the case, who asked not to be named, insisted Singh's death would not affect the ongoing trial.
"There is no reason for the case to suffer," said the officer.