Delhi gangrape accused Ram Singh's alleged suicide in the high-security Tihar jail, which houses over 12,000 prisoners, is the third such incident in the last 15 months.
Singh, the prime accused in the December 16 gangrape of a 23-year-old girl in Delhi, hanged himself from the grill of his cell in Jail No 3 using his clothes early on Monday morning, jail officials said.
The jail had reported a total of 18 deaths, including two suicides in 2012.
"There have been 18 deaths in Tihar jail in 2012, out of which 16 were natural while two were cases of suicide," said Vimla Mehra, Director General, Prisons, while addressing a press conference recently.
A senior jail official said Singh's suicide is the first such incident this year.
He said magisterial inquiries are conducted into every death that takes place inside the jail premises.
Considered India's largest and most secure prison, Tihar has a three-layered security system.
Surveillance and external security is with the personnel of Indo-Tibetan Border Police and the Central Reserve Police Force, followed by the Tamil Nadu Special Police, which mans various gates and frisks visitors.
Jail operations are taken care of by the personnel of Delhi Prisons.