Her 28-year-old male companion, who was injured in the attack, was called by the prosecution to testify Tuesday against five defendants in a special fast-track court in New Delhi.

"The star witness will be cross-examined today. Our questions will mainly revolve around his testimony and his identification of accused," AP Singh, lawyer for two defendants, said.

All of the defendants pleaded not guilty Saturday to the charges that include murder, gang rape, abduction, destroying evidence and criminal conspiracy.

They could face the death penalty if convicted of murder. A sixth suspect is to be tried in a juvenile court, and faces a maximum sentence of three years at a correction home.

The young woman was raped on a moving bus and assaulted with an iron rod in the Indian capital on December 16. She died in hospital of multiple organ failure two weeks later.

The attack triggered protests in New Delhi and other Indian cities demanding improved safety measures for women.