"The rape and murder of the young woman in Delhi last year was a horrific crime, and our deepest sympathy goes out to the victim's family. Those responsible must be punished, but the death penalty is never the answer," said Tara Rao, director of Amnesty International India. "Sending these four men to the gallows will accomplish nothing except short-term revenge."
Rao said there is "no evidence that the death penalty is a particular deterrent to crime, and its use will not eradicate violence against women in India."
Death sentences issued by Indian courts have rarely been carried out in the past decade. No state executions took place between 2004 and late 2012, when the last surviving gunman from the 2008 terrorist attacks in Mumbai was hanged.
But human rights advocates have said they fear India's stance on executions has changed.
"In the past year, India has made a full-scale retreat from its previous principled rejection of the death penalty," Meenakshi Ganguly, South Asia director at Human Rights Watch, said last month.
Two others accused
The fate of two others accused in the case had been determined before this week.
One man, Ram Singh, 35, was found dead in his jail cell in March. Authorities said he had hanged himself, but his family said he had been murdered.
A juvenile court convicted a teenage boy on August 31 for his part in the gang rape, sentencing him to three years in a special juvenile correctional facility.
His trial was in juvenile court because he was 17 at the time of the crime, and the sentence is the maximum allowed under the court's rules.
Many Indians, including the victim's family, expressed dissatisfaction with the sentence.
The same crowd outside the courthouse that cheered Friday's death sentence for the four adults turned their ire on the juvenile. The crowd chanted, "Hang the juvenile."
A lawyer for the victim's family said they would go to India's top court to contest the youth's sentence.
A rape every 22 minutes
As in many countries, rape is a grimly frequent occurrence in India.
According to Indian government statistics, a woman is raped every 22 minutes on average.
But the New Delhi attack seized the country's attention.
Advocates criticized the world's largest democracy for failing to protect half of its population. Protesters demanded better treatment of women and decried the apathy of police and the judicial system.
The government passed tougher anti-rape laws, introducing the death penalty for repeat offenders, and imprisonment for acid attacks, human trafficking and stalking.
But some Indians said that while the laws on crimes against women have changed, mindsets and enforcement have been slower to adjust.
'Take it to the source'
Government figures show the number of women reporting rapes has risen significantly since the New Delhi attack and the heavy scrutiny that followed it. Observers said it indicates women who are victims of sexual attacks feel more emboldened to come forward than they did before.
Prosecution of such crimes has improved, said Kiran Bedi, a human rights activist and former Indian police officer. But it will take a heavy emphasis on the family and school environments to resolve the problem in the long run, Bedi said.
"You can't just begin and end with the police and the prosecution and the courts," she said. "You have to go backward and take it to the source."