His parents and lawyer allege that he was murdered, and want the Central Bureau of Investigation (CBI) to determine how he died.
Jail authorities claim the 35-year-old committed suicide by using his shirt and threads from his sleeping mat to construct a rope, which he hung from a grille on the 10-foot-high ceiling by using a plastic bucket. But they are unable to explain how three cell-mates slept through the hanging in a tiny room. (Read: Three cellmates slept through Ram Singh's suicide, claim officials)
The family says that it is now concerned for the safety of Singh's brother, Mukesh, who is among four other men in prison at Tihar for the gang-rape case. The sixth suspect is a juvenile and is being tried and kept separately. (Read: 'Shoot us, but don't send us to Tihar': other Delhi gang-rape suspects)
Home Minister Sushil Kumar Shinde acknowledged that the death was "a grave lapse" and said it is too early to conclude that Mr Singh committed suicide. (Read)
Officials have no answer for why or how a guard, posted near the cell because Mr Singh was thought to be suicidal, missed what happened this morning. Jail No 3, where he was imprisoned, is reserved for death row prisoners and those who are being tried for highly sensitive cases. Wardens and others are meant to ensure close and constant monitoring of the inmates.
Though there are security cameras in this section of Tihar, none was positioned to film Mr Singh's cell.
The heinous assault on the 23-year-old medical student triggered street protests, tough new anti-rape laws and a national debate about the lack of security for women across India.
"I wanted him to be hanged...publicly. Him dying on his own terms seems unfair," said the brother of the student who died.