More than seven years after a 23-year-old medical student was gang-raped in a moving bus in Delhi, four men convicted for the brutal assault were hanged this morning.

The four men -- Akshay Kumar Singh, Pawan Gupta, Vinay Sharma and Mukesh Singh -- were hanged at 5:30 am at Delhi's Tihar Jail, hours after the Supreme Court, in a midnight hearing, refused to grant them relief and stay their executions. The four were hanged simultaneously, a first in independent India's history.

The four were convicted for the gang-raping and murdering a 23-year-old medical student, who came to be called Nirbhaya, in a moving bus in Delhi in December 2012. Nirbhaya subsequently died of her injuries.

A few minutes ago, the bodies of the four Nirbhaya convicts were lowered and checked by a doctor. As per protocol, bodies of convicts who are executed are kept hanging for 30 minutes before being lowered. The bodies of the four Nirbhaya convicts have been lowered and checked by a doctor who has declared all the four dead. The bodies will now be sent for post-mortem.

The crime took place on December 16, 2012, when a 23-year-old medical student boarded a bus in Delhi along with her male friend.

On board the bus, the woman and her friend were assaulted by a group of six people. The woman, who was gang-rape, died two weeks later. The brutal nature of the attack led to country-wide protests and forced the government to set up a commission to review the country's laws on rape and crime and against women. The commission's review ultimately led to laws prescribing stricter punishments for crimes against women.

Six people were accused of gang-raping and murdering the 23-year-old medical student, who came to be called Nirbhaya. Of the six, one was a juvenile and was convicted by the juvenile justice board. He served three years in a reformation home and was released.

Of the remaining five, one committed suicide in jail. The four others were convicted by a trial court and sentenced to die. The convictions and the death penalties handed to the four men were upheld by the Delhi High Court and the Supreme Court.