Significantly 33-year-old Ram Singh, who has a slight deformity in his right hand after an accident, hanged himself from the grill of his cell in Jail No 3 using his clothes, jail officials said.
The news of his death immediately triggered demands from his lawyers and family for a CBI probe. They alleged that he was murdered inside the jail and refused to believe that he could have committed suicide.
Since it was a death under suspicious circumstances, Delhi government ordered an inquiry by a Metropolitan Magistrate.
"Singh was not alone in the cell when he committed suicide. Other inmates were present and a guard was also posted. But nobody came to know about it. Around 5 AM, he was found hanging," a senior jail official said.
Also Read
Prone to violent behaviour and mood swings, he had suicidal tendencies and was under "suicide watch," he said.
"There is already an inquiry which has been ordered by Tihar Jail on suicide of the main accused. We are enquiring into the matter," R P N Singh, Minister of State for Home Affairs, said.
The girl was raped in the bus by him and his five associates, including a minor, in south Delhi after brutally beating her and also her male friend. The girl died in a Singapore hospital on December 29.