The prime suspect in the gruesome gang-rape and murder of a woman in the Indian capital in December was found dead in prison early morning Monday, authorities said.

Prison officials told Indian media that Ram Singh, the driver of the bus in which the physiotherapy student was attacked, hanged himself in his cell in New Delhi’s Tihar Jail at around 05:00 a.m. local time Monday.

The 23-year-old victim died Dec. 29 due to multiple organ failure, two weeks after she was raped on a moving bus in Delhi Dec. 16.

The incident, which shocked and outraged India, sparked massive protests across the nation and particularly in New Delhi.

The six suspects, including Ram Singh and his brother Mukesh, were charged Jan. 3 with multiple offenses including murder and gang-rape. The trial has been ongoing in a fast-track court. The charges could fetch death penalty. One of the suspects — a minor — is being tried by a juvenile court.

Ram Singh, 33, highlighted as instrumental in the crime, was accused of using an iron rod on the victim with the help of two other suspects, earlier reports had said.

Ram Singh hanged himself with his own clothes in his cell in Jail No. 3 of Tihar, CNN-IBN news channel reported citing prison officials. Ram Singh's lawyer, V.K. Anand, confirmed to Reuters he had committed suicide, but declined to furnish further details.

The physiotherapy student’s 20-year-old brother told Reuters: "He knew he was going to die anyway because we had and still have such a strong case against him.”

"I'm not very thrilled with the news that he killed himself because I wanted him to be hanged... publicly. Him dying on his own terms seems unfair. But, oh well, one is down. Hopefully the rest will wait for their death sentence."

In January, it was reported that the suspects were under “suicide watch” as the jail sources indicated that the five had been isolated in the jail by other inmates.

The Tihar Central Jail complex has several prisons, each identified by a number. Accused Pawan, 19, and Akshay, 29, are held in Jail No. 4, while Vinay, 20, and Mukesh, 26, are in Jail No. 7, CNN-IBN stated. A senior officer has been in-charge of overseeing the five. Other jail wardens were also on alert.

Singh's brother Mukesh has been informed about the incident.

Minister of State for Home Affairs R.P.N. Singh said his ministry has sought a report from the Delhi Police and that an inquiry has already begun by the jail officials.

The National Commission for Women (NCW) chairperson Mamata Sharma demanded an investigation into the incident.

“Suicide in a high security jail like Tihar is a matter of serious security lapse. The authorities must conduct a thorough probe to ascertain what led Ram Singh to take such extreme step,” she was quoted as saying by Zee News. She added that Singh’s death will not affect the trial.

Former Director General at the Bureau of Police Research and Development Kiran Bedi said: “When the case of the accused is in fast-track court, the accused is very vulnerable, he knows the end is very near. Such people become very introvert. Such a person is socially ostracized in the prison. Such prisoners need a strong watch.”