Nirbhaya case: The convicts were scheduled to be hanged today at 6am

The four men convicted in the rape and killing of a 23-year-old medical student in Delhi in 2012 will not be hanged today as scheduled, a judge in Delhi said on Monday, deferring their execution for the third time.

The mercy petition of one of the convicts, Pawan Gupta, is pending with President Ram Nath Kovind, so they have not exhausted all their legal options, the judge ruled.

"The condemned convict must not meet his creator with a grievance in his bosom that the courts of this country have not acted fairly in granting him an opportunity to exhaust his legal remedies," said the Patiala House court in Delhi.

For weeks, Akshay Thakur, 31, Pawan Gupta, 25, Vinay Sharma, 26, and Mukesh Singh, 32, have been filing staggered petitions challenging their death sentence in an effort to stall the execution.

The four men and two others, including one just short of 18, were arrested after the 2012 gang rape of a young woman on a moving bus. One of the main accused, Ram Singh, was found hanging in his jail cell in 2013. The teen was released after three years in a reform home.

On December 16, 2012, the medical student, who came to be known as "Nirbhaya", was on her way back from a movie with a friend when she was lured onto a bus. She was assaulted and tortured so brutally that she died days later, triggering an unprecedented outpouring of public anger over crimes against women.

"She was savagely raped and thrown on the streets. Her intestines were ripped out. And all these courts are sitting and watching a tamasha," Nirbhaya's distraught mother said outside the court.

Seema Kushwaha, the prosecution lawyer said, "Can't the court understand the manipulation of law? Our system is completely rotten. It takes years to get justice. We have to fix it together."

Last month, the central government approached the Supreme Court for a change in laws that it said were skewed in favour of criminals.

As the convicts filed petition after petition, timing them carefully to buy some reprieve, Pawan Gupta apparently waited till the end to make his move.

After his curative petition was rejected by the Supreme Court this morning, he filed a mercy petition before the President and went back to the Delhi court asking for his execution to be put off.

"You are playing with fire, you should be cautious," said the judge to Pawan's lawyer.

The hanging had been deferred twice before, on January 22 and February 1. On February 5, the Delhi High Court ordered that all four would have a week to exhaust all their legal remedies, including mercy petitions to the President, and said they cannot be hanged separately.