Four men will learn Friday if they are to hang for the shocking murder and gang rape of an Indian student after her parents begged for the "cold-blooded" killers' execution.

Three days after finding the gang guilty of a murderous assault which sickened a nation, Judge Yogesh Khanna will announce whether it fulfils the "rarest of rare" criteria for crimes that merit capital punishment.

There has been a huge clamour for the four -- Akshay Thakur, Pawan Gupta, Vinay Sharma and Mukesh Singh -- to be executed for their attack on a 23-year-old physiotherapy student and her male companion on board a bus on December 16.

After prosecution lawyers argued on Wednesday that the gang were guilty of a "diabolical" crime, the victim's mother implored the judge to hand down the death sentence.

"We beg the court that justice should be given to our daughter," said the mother, who cannot be named to protect the identity of her late daughter.

"It was not merely a mistake, they planned and killed her mercilessly," she told reporters.

The victim's father has said only the death penalty can bring the family some closure.

During Wednesday's hearing, defence lawyers argued Judge Khanna should resist "political pressure" and instead jail the gang for life, citing the youth of their clients who are all either in their teens or 20s.

The gang's relatives have also been pleading for their lives to be spared.

"I am hopeful that God will help us during the worst crisis in our life," Thakur's mother told AFP from the family's home in the state of Bihar where she has been praying to Hindu deities all week.

"There is no one except God whom I can trust for some relief to my son."

Handing down his verdict at the end of a seven-month trial Tuesday, Khanna found the men guilty of the "cold-blooded" murder of a "helpless victim" whose fight for life won her the nickname of Braveheart.

Feelings though are running high in a country disgusted by daily reports of gang rapes and sex assaults on children.

Since the convictions, newspapers have printed graphic details of the gang's onslaught against the young student and her male companion, including of the internal injuries she suffered while being violated with a rusty iron bar before being thrown naked off the bus.

Her injuries were so severe that she died nearly a fortnight later in a Singapore hospital. She briefly regained consciousness, telling family and friends of her desire to see her attackers burn to death.

India had an unofficial eight-year moratorium on capital punishment until last November when the only surviving gunman from the 2008 Mumbai attacks was executed. Weeks later, a Kashmiri was hanged over his role in an attack on parliament a decade ago.

Lawyers for the men have already said they will appeal the convictions in the Delhi High Court, which will spell years of argument and delays in India's notoriously slow legal system.

In appeal, the defence is likely to advocate lesser sentences for some of the gang, and argue that it was a "spur of the moment" crime rather than a premeditated murder.

There was widespread anger in the nation after a juvenile who was convicted last month for his role in the bus attack was sentenced to just three years in a correctional facility -- the maximum allowed by law.

The gang all lived in and around Ram Dass Camp, an unauthorised slum in southern Delhi where former neighbours have called for their execution.

"They deserve the harshest punishment... Reform is out of the question," said Maur Singh, a one-time neighbour who promised to hand out sweets in celebration if the judge sends the gang to the gallows.

"If the same happened to their sisters, would they give the perpetrators a second chance to reform? No, I don't think so."

Rattled by the mass protests, the government rushed through new anti-rape laws and ordered the trial be held in a special fast-track court to avoid it becoming a victim of India's notoriously sluggish legal system.

The home minister, Sushilkumar Shinde, has been quoted as saying the new laws "will ensure capital punishment for such a heinous crime" -- comments that defence lawyers say undermines judicial independence.

Senior opposition politicians have joined in the clamour while activists have protested outside the court, wearing hooded masks and mock nooses.

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