Delhi Police had charged the six accused, including a suspected juvenile, with rape. They later added the charge of attempt to murder.
This will now be converted into murder charge under section 302 of the Indian Penal Code, a police source told.
All six are presently in Delhi’s Tihar Central Jail. Police have said they were conducting tests to determine the age of one of the accused who claims he was not an adult.
The rapists hail mainly from a slum area in south Delhi. They coaxed the 23-year-old woman and her male friend to board the bus in Munirka in south Delhi Dec 16 night saying they were headed to Dwarka in west Delhi.
Once the bus began moving, they pounced on the woman and gang-raped her for some 40 minutes before dumping her on the roadside. She was also tortured with an iron rod when she put up stiff resistance.
Her friend was also thrown out of the bus and thrown out.
The bus passed through several key roads, even past Police Control Room vans. But since the bus windows were tinted and had their curtains drawn, no one could spot what was going on inside.
The two were discovered shivering and bleeding by a patrol of the National Highway Authority of India (NHAI) who alerted the police.
While the friend was discharged soon after, the young woman remained in critical condition in Delhi’s Safdarjung Hospital.
She was moved Thursday to Singapore where she passed away early Saturday at 2.15 a.m. IST.