India's Supreme Court today upheld death sentence awarded to the four convicts, who raped and killed a 23-year-old paramedic student in a moving bus in New Delhi in 2012,  terming the horrific crime as the 'rarest of rare', most brutal, barbaric and diabolical.

The case sent a "tsunami of shock" all over, a three-member apex court bench comprising Justice Dipak Misra, Justice R Bhanumathi and Justice Ashok Bhushan said.

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The bench, through a unanimous verdict, upheld the Delhi High Court judgment which had concurred with the trial court's decision to sentence the four persons to death, reports our New Delhi correspondent.

The top court said the act "demonstrates perversion of the accused" and added that if any case warrants a death sentence, it's this one. The court added that criminal conspiracy charge against the convicts stand established.

Those who will go to the gallows are Mukesh, 29, Pawan, 22, Vinay Sharma, 23, and Akshay Kumar Singh, 31.

One of the accused, Ram Singh, had allegedly committed suicide in the Tihar Jail while a convicted juvenile was sentenced to three years of punishment in a reform home.

The juvenile walked out of the reform home in December 2015 after spending three years there.

On December 16 2012, the young woman and her friend boarded a bus in south Delhi, assured by the driver that they would be dropped off at their destination.

The two were then attacked and the woman was gang-raped by six men and brutalised. She died in a Singapore hospital 13 days later.

The incident had sparked a nation-wide outrage and triggered weeks of street protests across India voicing concern over safety of women.

The Delhi High Court on March 13, 2014 agreed with the trial court finding that the crime of the convicts fell into "rarest of rare" cases.