According to a police official, Ram Singh, 33, the prime accused in the case committed suicide around 5.00 a.m. in ward no. 5 of Jail No.3 in Tihar jail.
"An inquiry has been ordered into the suicide incident to ascertain how Ram Singh committed suicide in the high security Tihar Jail," said G. Sudhakar, DIG (Prisons), Tihar Jail .
Singh, who had been charged in 13 cases in connection with the Dec 16 incident, had been facing day-to-day trial in a district court. He was supposed to be taken to the court Monday.
He had confessed to the crime, police said.
Singh was rushed to Deen Dayal Upadhyay hospital where he was declared dead.
On Dec 16, 2012, a trainee phyisotherapist was allegedly brutally gang-raped by Ram Singh and his five associates in a moving bus in the national capital.
She died of her injuries in a Singapore hospital two weeks later.
Photos: 'Godmen' who courted controversy
Photos: Kajol with mother, sister Tanishaa at Dadar Durga Puja pandal
Kareena Kapoor Khan snapped with baby Taimur at mom Babita's house
Photos: Amruta Fadnavis at a fashion and lifestyle exhibition
Photos: Sushmita Sen stuns in a black dress with thigh-high slit