Pawan Gupta and Vinay Sharma refused legal aid and offered to ''turn approver'', appearing as prosecution witnesses in the case.

They have said they will testify against their fellow accused in their trial, which is expected within days. But even if they did testify against the other three men - Ram Singh, his brother Mukesh and Akshay Thakur - it appears unlikely it will win them any mitigation.

Indian media quoted a senior policeman associated with the case: ''Even if they turn approver, it does not change our position right now, nor would it affect the outcome of the case vis-a-vis their culpability. They will be awarded commensurate punishment if held guilty along with the others.''

Police have asked for the death penalty for all five men.

The five men - a sixth alleged attacker is a minor and will appear before a juvenile court - were expected to appear in court for the first time on Monday afternoon, Delhi time.

Their case will be the first sent to a newly inaugurated ''fast-track'' court, created to hear sex assault cases more swiftly than India's overburdened and bureaucratic criminal courts.

The six are accused of luring the 23-year-old woman and her boyfriend onto a bus before locking the doors and beating the boyfriend unconscious with an iron bar. They then turned on the woman, bashing her with the bar and taking turns gang-raping her for more than 40 minutes.