New Delhi, Mar 12 (IANS): A day after the alleged suicide by Ram Singh, prime accused in last December's horrific gang-rape, police said Tuesday that his death would not affect the case and there was enough evidence to convict the other four accused men.

Police said that Ram Singh had died due to hanging. He was the driver of the bus in which the 23-year-old woman was brutally raped and beaten Dec 12 last year. She died of her injuries.

A doctor who took part in the autopsy said the 35-year-old had no external injury marks on his body.

Rattled by the death, authorities in Tihar have also placed the four other accused on "special watch".

"They are on special watch and an officer has been deputed to keep a tab on their activities," a jail official told IANS requesting anonymity.

Ram Singh, who reportedly committed suicide in Tihar Jail Monday morning, was one of the six accused in the rape of the young woman in a moving bus. A magisterial inquiry has been ordered into his death. His family alleges he was murdered.

Ram Singh was arrested Dec 17, 2012, a day after the brutal gang-rape that ignited protests all across India.

"Ram Singh's death has no relation with the further proceeding in the case," said an investigation officer.

A day-to-day hearing into the case is going on at a fast-track court here.

The other accused facing trial are Ram Singh's brother Mukesh, 26, fruit seller Pawan Gupta, 19, gym instructor Vinay Sharma, 20, and bus cleaner Akshay Thakur, 29. All are in Tihar Jail.

A panel of three doctors conducted Ram Singh's post-mortem at the All India Institute of Medical Sciences (AIIMS) before the body was handed over to his family. They took the body to Karauli district in Rajasthan for cremation.

An AIIMS source said Sanjeev Lalwani and D.N. Bhardwaj were among the doctors on the panel that conducted the autopsy. It started at 10.45 a.m. and took about two hours.

The Tihar authorities have decided to focus a CCTV camera on the cell of the four other accused.

"We are focussing a CCTV camera on their cell to increase surveillance on them," an official told IANS.

The special watch is meant to prevent the four from causing possible harm to themselves, the official said.

Two of the rapists, Pawan, 19, and Akshay, 29, are held in Jail No. 4 of Tihar Jail while Vinay, 20, and Mukesh, 26, are in Jail No. 7.

The officer ruled out the possibility of threat to the gang-rape accused from other prisoners.

The five accused were formally charged in the Saket fast-track court 18 days after they gang-raped and tortured the trainee physiotherapist, causing multiple-organ failure that led to her death in a Singapore hospital Dec 29.

The sixth accused in the case is a juvenile and his case is before the Juvenile Justice Board.