Lawyers for four men convicted of gang-rape and murder refer to independence leader during hearing ahead of sentencing

Defence lawyers cited the teachings of Gandhi as they fought to save four men convicted for their role in the gang-rape and murder of a 23-year-old physiotherapist in Delhi from execution.

Akshay Kumar Singh, a bus cleaner, Vinay Sharma, a gym instructor, Pawan Gupta, a fruit-seller, and Mukesh Singh, who was unemployed at time of the attack last December, were convicted on Wednesday of rape, unnatural sex, murder, conspiracy and destruction of evidence. They had denied the charges against them and their lawyers have said they will appeal the verdict.

AP Singh, representing Sharma and Thakur, spoke of what he said was the belief of the Mahatma Gandhi, the independence leader and pioneer of nonviolent political protest, that "God gives life and he alone can take it and not manmade courts".

The four men will be sentenced on Friday, a judge in the Indian capital said on Wednesday.

India has repeatedly voted against UN resolutions for a moratorium on capital punishment though it carries out only infrequent executions. Three men have been hanged in the last nine years – a rapist and murderer, and two Islamic militants convicted of terrorism offences.

Police officials told the Guardian that the four convicted men sang Bollywood musical songs while being driven from Tihar prison to the court on Wednesday.

"They were totally relaxed [this morning]. Mukesh sat in front, the rest behind and they were humming songs," said one police official, who accompanied the men.

One of the four shouted: "I am innocent! I am innocent! I am innocent," at reporters as the bus passed the gates of the district court of Saket in south Delhi where the seven-month trial had been held.

Judge Yogesh Khanna heard arguments for and against the death sentence during Wednesday's session. Prosecutors have insisted that the case qualifies as "the rarest of the rare" which justifies the severest punishment. The judge, however, can order life imprisonment.

AP Singh, representing 19-year-old Sharma, reminded the court of his client's youth, while Thakur's lawyer argued that the 26-year-old had a young son and ill parents.

Prosecution lawyers stressed what they said was a premeditated attack to murder the victim and a male friend by running them over after they were dumped, apparently unconscious, from the bus in which they had been assaulted.

The family of the victim, who died from massive internal injuries caused when she was penetrated with an iron rod in the attack, have called for the death sentence.

Sushilkumar Shinde, India's home minister, told reporters in Mumbai on Tuesday that a death sentence was "assured".

The comments, which came after the verdict but before sentencing, were unusual and an indication of the Indian government's concern about public anger over the incident. The public appears overwhelmingly in favour of execution of the men.

But Colin Gonsalves, a prominent human rights campaigner, said the men should receive life sentences, not death.

"Popular sentiment is guided by people at the top and those at the top are very bloodthirsty kind of people. You can see the spread of hatred and violence in this country," he told the Guardian.

The trial of five of the attackers started in February. One defendant, a bus driver, hanged himself in prison in March. The oldest of the six accused of the attack on the physiotherapy student was alleged by police to have been the ringleader. The youngest, who was 17 at the time of the assault, was tried separately and was last month sentenced to three years in a juvenile reform home – the maximum punishment of a minor under Indian law.

The attack provoked outrage in India with protests across the country. It also led to an unprecedented national discussion about sexual violence and calls for widespread changes in cultural attitudes and policing, and legal reform. The international image of the country was damaged, with numbers of female tourists dropping significantly.

Relatives of the convicted men have spoken out against the verdict. "If he would have been a politician's son this would not have happened with him," Vinay Sharma's mother told reporters.

The prosecution case relied on testimony from 85 witnesses, a statement given by the victim before she died, DNA samples, dental records from bite marks on her body that matched the teeth of some of the men and the evidence of her male friend, who was also badly beaten in the attack.

He described how the couple were attacked after boarding the bus on the way home from an evening film at an upscale shopping centre.

The victims were eventually dumped at a layby on the outskirts of Delhi, and the woman died two weeks later in a Singapore hospital. Her ashes were later scattered in the Ganges river, near her ancestral village in rural India.

The accused men were also found guilty of robbing another man earlier in the evening of the incident.

Police described how the six had set out from the Singh brothers' home in a bus on a "joy ride". They then tricked the victim and her friend into boarding the vehicle and assaulted them shortly afterwards.

Laws on sexual assault and harassment were tightened in the aftermath of the incident, but serious institutional reforms will take much longer, women's rights campaigners say.

Police in Delhi believe a rise in rape reports is partly owing to an increased willingness by victims to come forward. There were 1,036 cases of rape reported in the capital in year to 15 August, compared with 433 in the same period last year, according to police data.

Gang-rapes, acid attacks and other acts of violence against women continue to be reported across India each day